I do a weekly litter pick on my local trail. Finding inner tubes hanging in trees and bushes is quite common. Last week found two plus the empty box. The most common litter is plastic energy drink bottles, usually Lucozade followed by Red Bull and just dropped on the trail. Those with a slight feeling of guilt try to hide their rubbish behind a log or rock! Gel sachets are found all along the trail usually with just enough of there sticky contents still in side to run out all over my gloves.
I find bike debris littering the trails most common are reflectors followed by mudguards, rear lights and surprisingly glasses. It’s also surprising how many empty cigarette packets are found, usually at the top of an uphill section.
Anyway I’m just about to go out now to do my litter pick.