There are literally millions of collectors and hundreds of thousands of collectable items. Most spring from some form of childhood memories associated to happiness, better times, fun and being able to relate to some thing. You may start by saving your hockey cards from when you were growing up. Most people refine their collections over time. What started off as collecting every hockey card you could eventually morphs to your favourite team, or player or every card from the year you were born or whatever other criterion you decide is important. It is simply impossible to collect everything.
Then there are the extreme collectors. Example: Syd Bolton of Ontario. In his own words " I am a complete tech freak". Syd turned his love of all things computer into Canada's largest collection of computer and video games. His hobby has actually become a museum. Syd has over 45 active computers from over 1000 in his museum, from the 1st ever personal computer to Atari, Coleco, and pretty well every variant between. He has over 25,000 video or computer related items.
All this in his house. Every room is dedicated to computers, video games, consoles, and all things geek. Syd's collection is valued at over $1,000,000. Your collection may not go to this extreme, but you have to admire the dedication...and yes, he has a girlfriend.