It's really up to you but if you have a 24 hour supermarket nearby then there's really no need to have formula in, as you can always go and get it if you need it.
I would recommend getting a couple of stretchy sleep nursing bras once you get to 37+ weeks or nursing tank tops with support. Expect your cup size to increase and your band size to decrease but if you get the stretchy ones, they tend to cover a few sizes so you should be OK to guess. I'm having a summer baby too and I think I'm going to go for the tank tops this time as they'll be useful for the hot weather.
Breast pads are useful, as is a waterproof mattress protector for your bed, or at the very least a towel under the sheet on your side. Some people leak more than others. I used washable pads and have got more for this time.
You can get Lansinoh or wait to see if you need it. Your midwife might be able to give you samples, and a little goes a long way.
Some people find a feeding cushion is helpful but you don't strictly need this if budget is a concern. You can often find them second hand. I agree that muslins are much more useful than bibs.
I'm planning to get a pump and bottles later, because if I need one in the early days I can get one from the hospital and potentially hire that out, then later on I'd get one according to my needs - if only to be used occasionally, then a cheap single hand pump ought to do. If I was going to go back to work at 4 months or something, a double electric one might be more useful.