Don't laugh. These are very useful for cutting foam into basic shapes before using the grinder. Also great for trimming excess foam when you intentionally use a piece of foam larger than you need, adhere it on the seat, and then trim it to size. You'll use this over and over again, no doubt.
4-1/2 inch grinder, preferably with variable speed, is used to shape your foam. The variable speed is nice if you want to carefully feather the foam or remove small, incremental amounts. In these cases, you would simply set the grinder to a lower speed.
Grinder Sanding Pad and Disks
To use with the grinder, you'll need a sandpaper backing pad, along with low abrasive sandpaper (e.g., 120 grit). If you don't have, or can't find, smooth grit sanding discs, take your coarser sanding discs and grind away on the pavement, bricks, or something similar until it's smoothed out. If the sanding disc is too course, the grinder will take off foam too quickly, making careful, smooth shaping really challenging. The disk can have almost no grit to it and work great.
Commercial Foam Cutter
A commercial grade foam cutter like the Bosch in the pic cuts through foam like butter, making quick, smooth work of cutting and shaping. Unless you're doing this all the time, however, it's hard to justify a price tag of over $300.
An air stapler makes driving staples into the seat pan so much easier, especially if it has an extended tip (to place the staples in those tight spots under the seat pan. As with most tools, prices range from a lot ($300+) to $20 at Harbor Freight. Truth be told, I use the $20 version, and it works great. An electric heavy duty stapler is a little trickier to use given its shape and flat nose, but it works. Unless you're using an unusually thick seat covering, 3/8" - 1/2" crown and 1/4" length staples do the trick. Check out the picture above to understand staple crown and length.
Spray adhesive is used to bond pieces of foam together before shaping them. Although the seat cover holds the seat foam firmly in place, you'll definitely need this if you use multiple pieces of foam. Higher quality products, such as the 3M spray adhesives, will give you quick, strong bonds. The less expensive "hobbiest," all-purpose sprays will probably end up causing you more hassle than value in money saved. For some informative info on 3M spray adhesives, click <a href="docs/3m_adhesives_brochure.pdf">here</a>.
Respirator or Dust Mask
Grinding foam can produce some serious dust. Don't do it in the kitchen, and make sure you wear a mask. You'll be happy you did.
Simple tack puller is for taking out the staples that secure the seat cover to the seat pan. Yeh, yeh, you can use a screw driver, but a tack puller makes it easier and is cheap. I know I'll end up tweaking the foam several times before I like it, so it's worth a buck or two to me.
Needle Nose and Diagonal Cutter
These make removing staples from the seat pan so much easier. After you loosen the staples with the tack puller, just pluck them out with one of these. I personally like the diagonal cutter better, as its sharp edges grab the staple more securely. If I can't loosen a staple with the tack puller, you can pretty easily pull it out with the diagonal cutters.