I usually carry a Glock G19 and a spare mag. 30 rounds total. When I carry the full sized 1911 (.45) I bring along one or two spare mags, 16 or 24 rounds total. With flash mobs (on bikes or not) becoming more common I’m thinking of adding another mag to my standard carry, or maybe just having a couple in my car.
At one time you could get 15 round magazines for a 1911 45 ACP....I still have 5 of them. They work pretty well, but it is not something you can carry concealed.