I love this question because of I have been a collector of whatever interests me my entire life. That is not to say I'm a pack rat because I do minimize at times, but I'll start by giving you some examples of what I've collected through the years. I have collected precious rocks, and rainbow obsidian is my favorite. They can get quite pricey, or you can choose to collect rocks the old-fashioned way. How I collected them was by going to different trade shows and stores when I traveled.
I also enjoyed collecting comic books at one time, and most of my comic books I now have are first edition, albeit from the 1990's. Records are fun to collect, and I am also a huge collector of baseball cards and baseball memorabilia. My latest collection, and this is one I highly recommend if you have the opportunity, is collecting seashells and shark teeth. There are so many different things you can do with them. If you make crafts or jewelry with them, you can enjoy them and also give them to family and friends. Stamps are another fun item I was collecting for awhile, and yes, I still have my collections.
Each collector is different, but those were my choices throughout the years. I'll tell ya, the most rewarding collections are things you can find without paying for them, hence the great time I've had collecting seashells and shark teeth! Shark teeth have value, and so do shells. The best thing is to find something you like and really enjoy.