Old matchbox labels. I try and get a full set in a series, which is maybe 10 designs, then frame them - not really a collection in some senses I guess but erm, it sparks my interest enough.
Not at home so don’t have them to hand but I’ve got a full set of Soviet space ones for example from the 60s. They are often very cheap.
A couple of semaphore signals with spectacles and lenses are mounted in the garage, a semaphore shunt dummy, class 25 cab desk and various bits that were liberated from the skip at work from class 313s are in a box in the garage, including a guards panel from a 313.
To much annoyance of the wife I have a class 37 speedo on display in the bedroom along with a fair few original posters framed and on the wall which are my favourite, including an original 80s InterCity sleeper poster.