Your shop and machinist experience suggest you can start by stocking raw materials (though you may already have access to plenty via your metal shop program). Some materials we have frequently used include 1/8" and 1/16" wall aluminum box channel, 1/8" wall aluminum angle, 1/8" and 1/16" thick polycarbonate sheet, various sizes of PVC piping, and 3/8" 1/2" and 5/8" steel drive shafted (we used keyed, but others prefer hex). Depending on your exact facilities and expertise, you may opt for other alternatives. Some teams invest heavily in sheet metal designs, while others weld round tubing, for instance.
However, depending on your skill and experience in terms of design (and CAD), you may also want to stock up on some more COTs and ready-for-use options as well. 80/20 (or similar) and/or
VersaFrame are great options for teams that "design on the fly" and need the ability to iterate on their final machine.
Regardless of the route you chose, ensure you have the proper hardware to use. At the very minimum stock up on #8, #10, and 1/4-20 bolts and nuts of various sizes. Also ensure you have bearings and/or bushings to use for your shaft sizes, shaft collars, #25 and/or #35 ANSI roller chain, and any special hardware for any extrustion you want to use (like 80/20 t-nuts). Rivets may also be worth investing in, depending on your manufacturing techniques.
Many basic electronics should be covered by your rookie Kit of Parts. However, you may end up wanting to buy additional motors and speed controllers beyond those. We cannot guarantee the rules on any of these components until they're released. However,
AndyMark,
Vex, and
Banebots have historically been the vendors for any additional motors not included in the Kit of Parts (or included in quantities less than the max allowable via the rules).
Those same vendors are also useful for many other COTs components, including gearboxes, #25/35 plate sprockets, drive pulleys, wheels, hubs, etc. The KoP will include enough to get you moving (and should be the basis of your design as a rookie team), but consider purchasing some additional materials for use on your manipulator components or to upgrade your Kit of Parts drive base. Planetary gearboxes are often useful for end-effector mechanisms, for instance.