To quote everyone else, get whatever you can find coz they're all useful. Some of my most commonly used ones the small plastic "clothes peg" types that I picked up from a dollar shop. I also use some cheap sliding clamps about 10" long, and some heavier G clamps I found in the hobby section of my local hardware store. It's also a great idea to get some lead shot (or even sand), fill a couple of zip-lock plastic bags with it, and put the bags in old socks to use as "soft weights" for holding down sheeting while it dries. Masking tape is very useful too - get a couple of rolls, and if you can get packing straps they're great for holding slabs in place (eg: round the curved edge of a firewall) till the epoxy dries.