COOL TOPIC!! In regards to nomads/or sedentary tribes stashing staves:
I agree they probably all had two bows each. In regards to the staves, I also believe they would have had several stashed away. You don't have to carry it with you (plains tribe or not), and perhaps its a better to stash away in a safe dry place; benefits of this: don't have to carry it around, wont loose it, wont get stolen, someone else you trust can get it, you can think of all the other possibilities. For nomadic people you were usually moving in a circular pattern, or at least staying within a region. So riding your horse to the rock outcrop where your bows are stashed, after breaking your last bow, would be quite efficient and effective.
I doubt few tribesman didn't have several backups of already made bows, and staves.
A comparison to this can be made by a biface cache that was found where I live. Cant say where due to legalities (I'm an archaeologist). Its was a cache of over 100 obsidian biface blanks - pre forms, also called trading blanks. These people were constantly on the move -Western Mono from the foothills, valley floor, and to the mountains. The cache was in a random spot you would have never guessed to look in a million years. Uncovered by large machinery. My point is they didn't carry all these tools with them, they would be stashed about at camps and other secretive places or places of power.
I'm new on here by the way. And really enjoying the topics!