Seriously, get the biggest, nicest pot/kettle you can afford. If you're getting into kegging right away, clearly you're not shy about dropping some cash on this hobby you haven't tried yet (don't worry, you'll like it), so don't buy something you'll immediately have to replace. A 5 gallon pot isn't getting the job done for anything besides partial boil extract batches. 7-7.5 gallons? Good to go for AG. 8 Gallons? Better. 10 gallons? Great. 15 gallons? Awesome. Valves/fittings on there too for pour-less transfer? Set for life.
One other super cheap thing not included in most kits is an auto-siphon. Best 10 bucks you'll ever spend brewing. Get one. A nice luxury would be a stir plate and a big 2-4L erlenmeyer flask. If you're making starters and controlling your fermentation temperatures from batch one, you'll be making better beer than 60% of all homebrewers right off the bat.