I think I’ve come to realize that the useful training tools seem to be:
-half cut tennis balls
-straps (for lifting)
And, except for the mp3 player, you can get all of that for under $300.
Is there much else besides this, outside of obvious equipment (spikes/blocks/etc.)?
If I was marooned on an island; I would say all you need is an mp3 player and a bottle of caffeine.