I was just thinking about all the card games I know how to play with one or more regular decks of cards. I know how to play:

Canasta
Rummy
Progressive rummy
Poker
Blackjack
99
Kings-in-a-corner
The bum game
Speed
War
Go Fish
Old Maid
Solitare
Double Solitare
Eqytian Ratscrew
Hearts and
Spades.

At one time or another I could play:

Hand-and-foot
Gin Rummy and
Crazy 8's.

Using specialty decks, I can play:

Uno
BombO
SkipBo (made by the same company) and
Phase 10.

Imagine what I would know if I didn't remember all those rules!!