Here is what I try to keep on hand.
1x1 Aluminum Square 1/16" Wall - Metal Distributor $15/21'
1x1 Aluminum L 1/8" Wall - Metal Distributor $12/16ft
1/2" Hex Shaft - VEXpro
1/2" Tube Axle Stock - VEXpro
PVC, Plywood, 2"x4"s, Hardboard for prototyping
1/16" Lexan - Plastic distributor about $55 for 4'x8' sheet
.09 aluminum sheet metal, we get scraps from one of our sponsors
#35 chain, master links, & half links
Bolts, rivets, lock nuts, we use #10-24 and 3/16 rivets
Wire it works well and is cheap, we normally use better 10AWG for motors
12 AWG Monoprice 50'
$16.58
18 AWG Monoprice 100'
$10.36
6 AWG wire for battery connectors emergencyelectricpowersystems. 1' $0.84
http://goo.gl/ylnhQ (We actually used 4AWG last year for our 6 CIM drive)
PWM cables and connectors to make custom length wires normally from Hansen Hobbies but other places as well.
We use Anderson on every motor, but on the speed controllers we switched to the spade tabs and connectors
Mouser #
571-42117-2 &
571-45204472
Polycord like others have mentioned
Conveyor tread like rough top, McMaster sells several varieties, good for grippers and rollers as well.
Zip ties, velcro, dual lock, double sided tape, gaffers tape, masking tape
Various plastic (ABS, Lexan, delrin, nylon) tubes for rollers and spacers
That's most of our normal stuff, there is always other things around like constant force springs, and sheets of plastic or metal from other projects.