While you have the money and time to spend on yourself buy some really good classic clothes that will last you, as you'll be in scruffy leggings and puked on tops for a while, and then unless you're well off, too broke to buy from anywhere finer than H&M or Primark. It took me eleven years to be in a position to afford some good cashmere sweaters, a grown up handbag (not designer, just well made) and boots.
I agree about gigs, theatre, lazy mornings in bed, brunches etc, and doing stuff on the spur of the moment. Some babies are easy going and you can just head off with them, but if you get one who is colicky or has reflux or shouts a lot then you have to plan outings around nap times and feeds.
I'd go on an adventurous holiday too. DH and I didn't travel abroad with DC until they were 8 (except for Eurodisney) as DS2 was quite unwell for several years and we didn't dare be too far from hospitals. I was absolutely craving some real travel by the time DC hit their teens, but at least we had some good adventures to reminisce over.
That all focuses on what you can't do. Don't underestimate what you can do. They give you a perfect excuse to head for fairgrounds and steam trains and corn mazes and circuses and Easter Egg hunts, to go sledging and build snow men and snow forts and paddle in rivers, build dams and dens, climb trees, have water pistol fights etc etc. You'll have a brilliant time with them, just a different kind of brilliant time.