I'm making this a page for all the tools I use. I'll update as I get more supplies.
Safety first right? Replacing safety equipment is a lot cheaper than hospital bills.
Gloves. Protection for your hands is essential if you're working with fiberglass and resin, but it's also nice to have gloves when doing other tasks so you can keep your hands clean.
Respirator. If you're working with anything that has fumes, you'll most likely need a NIOSH approved filter that filters out organic solvents. I've heard people say things like "Working with resin is fine without a respirator as long as you're in an open area." I'd personally rather not take that risk. This is also really good to have when sanding since you don't want those particles to go into your lungs. A respirator isn't that expensive and you can just replace the filter when you can start smelling fumes through it.
Safety glasses. You'll want safety glasses when you're sanding to minimize the dust that could get into your eyes. It's also good to protect your eyes when working with power tools or sharp objects.
Adobe Photoshop. You can use any image editing program really. I use this to put together reference images for getting scale correct. I get a lot of reference images before I even start the project so I can plan it out.
Adobe Illustrator. Unlike Photoshop, Illustrator is vector based which means you'll have something that can scale up or down without any loss in quality. It's also easier to design large things you can print out 1:1 scale without a huge file size since it's just points and lines.
Blender. I use this to make 3D models of objects. It's essential to have some sort of 3D modeling program if you're making your own Pepakura models.
Pepakura. This is a Japanese program that was originally designed for papercraft. It takes a 3D model and unfolds it to a 2D design so you can print it out, cut it out, fold, glue, and you have a 3D model. It's really useful for something where you need symmetry.
Hobby mat. This is a really handy thing to have so you don't cut into tables. Be sure to get the self healing mat so you don't have to replace it. The mats usually have a grid, rulers, and other things printed on but I don't really find myself using them much.
Ruler. I have a metal ruler from an engineering class during undergrad and it's really useful for measuring and doubles as a straight edge. Unlike plastic rulers you won't gouge the edge using hobby knives even if you slip.
Hobby knive(s). I got a set from Harbor Freight a few years ago for pretty cheap. It comes with three different handles and a lot of blades. The smallest size one broke on me since the piece that holds the blade is made out of plastic. It's not bad for the price but having an all metal X-acto handle isn't a bad idea.
Scribing tools. Another thing I picked up from Harbor Freight. It's made of metal and has a pointy tip so you can use it to scribe lines in things.
Utility knife. This has similar uses to the X-acto but usually has a longer blade. I use this to cut sintra since sintra is harder and thicker.
Sandpaper. You will need to sand down things if you plan on painting them. Get a bunch of various grits of sandpaper. When you're sanding things work from lower numbered grits to successively higher grits. This takes time but will let you get the smoothest finish. I have sandpaper from around 150 all the way up to 600. I have some hobby grade stuff at 1500 grit that I use for plastic models but haven't really used outside that application.
Sanding block. Use a scrap piece of wood or some other hard flat object if you're sanding flat areas. If you're sanding curved areas you may want to switch to something more flexible like a sponge. The sponge allows you to get around curves and maintain that shape as you're sanding.
Brushes. I picked up a box of 36 1" chip brushes from Harbor Freight for around $7. When working with resin it's handy to use a brush and toss it when you're done. You can also get small painting brushes from Walmart for pretty cheap.
Plastic cups. Useful for mixing resin and other things. Not all plastic holds up to resin though so you need to be careful. I mix resin in an old yogurt container I have and it's great since it's flexible and you can just pop out the resin when it cures - nice and clean for the next batch.
Glues/adhesives. I use white glue for gluing together cardstock for Pepakura work. I use superglue for a variety of things. I've also used Gorilla Glue in the past (you just have to watch out since that stuff expands as it cures). Epoxies and wood glues have their uses too so just pick the right glue for the job. When in doubt use the strongest appropriate glue.
Clamps. I picked up some clamps at HF for pretty cheap. I have both the regular clamps and the bar clamps (the 12" ones are always on sale for like $2 each).
Masking tape. You'll probably need to mask areas off when painting so pick up some masking tape. A lot of people really like the blue painter's tape since it doesn't leave residue and generally won't pull up paint.
Dremel. This is like the essential hobbyist power tool. I got the Dremel 4000 with several attachments. The one that is probably the most useful is the multipurpose one and you can also adjust the depth of it.
Electric sander. I picked up a refurbished random orbital sander from an outlet store for about 1/3 off the price of a new one. A random orbital sander has two motions - it rotates and also shakes around randomly in the horizontal plane. These two motions drastically reduce the presence of scratches and makes it easier to get a smoother finish. Pick up an electric sander if you want to save time and arm/hand strain from hand sanding the entire time.
Heat Gun. I got a heat gun at HF for under $10. This is useful for heating up styrene or sintra so you can heat form them. Don't get the heat gun too close to the plastic or it'll make it bubble a bit and release nasty fumes.
Sintra. Sintra, also known as closed cell PVC foamboard, is a rigid plastic that's used a lot in the making of signs. I have a sign place in town that lets me have some. They can come in a variety of colors but I just stick with the white stuff. The sintra I get is 1/8" thick. You can use a heat gun to shape it into more complex shapes.
Cardstock. I have a ream of 110 lb. cardstock for doing Pepakura work.
Resin and fiberglass. This will give your pieces some strength. For fiberglass I've only used cloth so far. The advantage of the cloth is that it's easier to get around curves, but fiberglass mat is stronger which means you probably won't need quite as many layers. With fiberglass cloth, try to lay down successive layers in offset directions so the fibers can impart more strength. Some people use spray adhesive to lay down the fiberglass, but you can also just coat the area with some resin before laying down the fiberglass. Make sure to wear a respirator when working with resin as it's very toxic stuff.
Body filler. A lot of people use Bondo brand body filler which can be found at most places including Wal-Mart. It's the cheapest body filler out there and you get what you pay for. I had a quart of the stuff and when that was running low I sprung for some Evercoat Z-Grip. It's $10 more for a gallon but I think it's definitely worth it since it goes on smoother and sands easier.
Spot putty. This goes hand in hand with body filler. Spot putty is thinner than body filler and you can get the one part version meaning it air dries and you don't have to mix in catalyst. Use this for repairing smaller pits. Spot putty will not hold edges well since it's not as strong as body filler.
Primer. I like to use Rust-Oleum automotive primer. It's got a light gray color and goes on pretty smooth. I've recently picked up some Krylon Ruddy Brown primer since it's cheaper and it works just as well. You can use just about any brand primer.
Spray paints. I normally get paints in rattle cans just because it goes on really smooth and you don't leave brush marks. A tip with spray cans is to put it in a bucket of warm water for about 10 minutes before using it. This increases the pressure inside and allows you to get a smoother coat of paint.