I have always carried a Swiss Army knife on me up until this modern day daftness where it now goes in the hold.
Infinitely useful many times and more importantly the potential to be.
I've been traveling commercially and on offshore helicopters for 40 plus years now and have seen a case in a helicopter that flamed out after lifting of from a satellite platform in which one guy drowned as his seat belt buckle was twisted and he could not get it open in time. Maybe if he had access to a small knife it could have turned out differently.