I have a somewhat large stockpile, partly because I'm of the same mindset and partly because I keep putting off work that I'd like to do.
As for what to stockpile, it really depends on what your end goal is and what the vehicle is due for. I'm interested in keeping rust at bay and overall aesthetics, but mainly in keeping this vehicle going, in good working order, for as long as I can. My stash consists of suspension parts (the entire front suspension including UCAs/LCAs,), brakes, exhaust, mounts/bushings/hardware, hoses and clamps of all types, various seals and gaskets, a throttle body, various sensors, filters, etc. I'll be putting together a stash for an upcoming timing belt job, at which time I'll pull the intake manifold and do the starter, all of the pulleys, fan bracket, and more.
I keep a big Word file of all of the parts I've ordered so I don't order something twice!
Edited to add a link to my
Baselining List.