I’ve seen some really lovely side paths like you’ve described, and the owners have put a narrow deck in – looks really fab. Have a play on houzz.com as it’s nice to see pictures.

do what you like to do. be wary that gravel, pebbles etc will end up everywhere especially with littlies (it will drive you insane!) how much sun do you get there? is it shady? maybe concrete and put some plants in pots there or herbs etc. then the space becomes useful.

We have the same. I just leave it as it has no impact on the remainder of the garden. Paving etc is quite expensive. If I had a choice though, I would concrete as weeds will take root in all other options.