I like to have a separate pair of gloves for the approach, then two pairs for climbing (i always keep the non in-use pair inside my jacket to stay warm) and a pair of big fluffy mittens for belaying. My "system" works like a charm for me.
Buy a couple of pairs, rotate them often always keeping the ones you aren't wearing inside your jacket so they don't freeze
An alternate spot for backup gloves/mittens is in your gaitors. The gloves/mittens stay very toasty and they help keep your legs warm too. And if in your gaitors they are very accessible when sitting in your harness. When climbing waterfall ice, or mountaneering, or even when cold weather hiking, my backups live in my gaitors.