Asthma puffer - they are cheap, and if someone has an asthma attack (and you can have one if you don't have a history) it saves a person's life. I have one in my backpack, just in case. This was a tip from a first aid course I did years ago.
I have severe asthma which has since been controlled with other medication. Fairly recently I gave mine to a lady who was experiencing an attack so can definitely vouch for this