Stockpile

[Nemo]

Some things that are cheaper if you buy in quantity:

12 AWG Machine Tool Wire (Red + Black spools) (McMaster-Carr)
Fasteners (especially 8-32, 10-32, 1/4-20) (Fastenal or whomever)
Polycarbonate 4'x8' sheet (local plastics supplier)
Aluminum 4'x8' sheet (thickness of .125" or so) (local metal supplier)

Things that I buy strategically with an eye on having a stockpile and reusing in future years:

DC Motor Controllers
Other control system components for 2nd robot
VersaPlanetary gearbox parts
Pneumatic Solenoids (FIRST Choice every year)