>> STOCK UP ON ESSENTIALs <<
Whenever you go to the hardware store after a few bolts/nuts/whatever, always buy at least twice as many as your job requires, even if you don't think that you could possibly ever have need of one again.
Keep these extras in an appropriate organized manner, such that they can be found should they ever be needed again.
A few extra pieces are always cheaper than having to make a special trip back to the store to replace the one that got flipped out into the bushes, never to be seen again.
Also, should you need the same thing again, no trip into town will be necessary.
I never leave TSC without at least twenty pounds of miscellaneous bolts/nuts/washers, which I keep stored in jars; I can take care of most projects without leaving the shop.