Probably un-exciting compared to some hobbies posted here but i dabble in some coin collection, have numerous lots of silver based items so initially some value there and quite a few 50 cent themed pieces too.Have a HSV themed penny collection too which is pretty cool if you like the brand will any pieces make me rich?..nup but some nice pieces nonetheless.
PNC's(postal numismatic cover's)with uncirculated quality coins are a thing too due to the low quantities issued, whereby you go to a stamp and coin show and buy a themed item stamped for that specific event and of which there may be a max of only 120 issued.If one keeps these things pristine and you can get them graded too(this is well worth the money spent i have noticed)some increase in value is there for sure..they usually sell straight after the event on ebay for around a 250/300% markup as a guide.