Realistically, how much stuff does your pup eat off the ground on walks?

our 4 month old australian shepherd hoovers up every piece of mulch, dirt, acorn, stick, etc. he can find, despite our hyper-vigilance - she's just too good/quick

obviously drop it and prevention isn't going to work 100% of the time, so realistically, how much non-food junk does your pup consume per day? and how much is too much or dangerous? considering it would be a hefty vet bill, how much junk is likely to cause a blockage?