I collected stamps and coins in the past. These were common enough hobbies when I was growing up.
In the case of stamps, I collected first day covers and bought stamps that came in packs from shops. I cut up stamps from mails in the past before electronic mails took over our lives. I soaked these stamps in water in order to peel them from the envelopes. These stamps were then dried and placed in a stamp album.
As for coins, I collected coins of countries we visited. I too bought commemorative coins, like coins for Chinese New Year. One example was the coin for Rooster Year in 1993.
I have stopped buying to keep items. However, I still cut up stamps on envelopes received through the mail if I found them pretty.