What do you need if pumping?
When I was still out on maternity leave, I managed fine with a hand pump (Medela Harmony) and a handful of bottles. The hand pump is nice to have on hand because if you end up having some oversupply and baby sleeps a bit long, you will want some way to relieve engorgement, and I could keep the hand pump by my bed and quietly use it as needed without waking anyone else up.
However, when I went back to work (~6 months) I ended up having to buy a double electric pump (I got a Hygeia Enjoye) with a hands-free pumping bra. I ended up pumping until DS was about 20 months (probably could have stopped a bit sooner but my MIL was very insistent he needed bottles) so it got a ton of use. So if you think you may at some point need to do more heavy-duty pumping you should definitely plan ahead.
For transport and freezer storage I really like the Lansinoh freezer bags and I have a small soft-sided cooler with ice packs. Then when I would get home I would lay them flat until they froze solid, and then you can either put them in a bin to hold them in order by date, or I would then put them in ziploc-type bags organized by date (weekly or monthly depending on how much you pump).
Also for being out and about I like having the Medela quick-clean wipes because it's not always easy to get to a sink to clean up.
For at home it is handy to have some baby bottle-specific brushes which I used for both the bottles/nipples as well as some of the pump parts, we also got a separate drying rack for bottles/pump parts. First time use and from time to time you need to boil everything but I didn't find it necessary to do every single time. You can also get microwave bags from Medela to sterilize instead of boiling, if you prefer.
DH (and nanny) found it super helpful to have a bottle warmer, we got the Munchkin brand one.
Depending on the pump you get and your pumping needs, you may want look into options for a battery pack vs. power supply for wall outlet vs. power adapter for car. Mine has a rechargeable battery so I just had to plug it in at night which was convenient.
And if your pump has a separate kit for horns/collection bottles/tubing/valve/membrane etc then you may want to have a spare or two on hand. Some women end up needing a different size other than the standard (this depends on the pump) so that is also something to keep in mind.
And if your pump doesn't come with a bag then you will want to have something that holds it and all your accessories for carrying it around, at least if you are going to pump when out and about.
Also general breastfeeding supplies:
Lanolin or something else for sore nipples, I used the Earth Mama Angel Baby nipple butter
Mother's milk tea for increasing supply as needed
Nursing pads as needed
Nursing bras/tanks as needed
Some mamas find a nursing pillow very helpful
The above pretty much covers it. I was an EP'er the last time around (hopefully not this time, that was pretty much the third level of hell for me) and worked full-time from about four months on, so all of this maybe overkill for you but perhaps someone else might like the info.
I had a Medela Pump in Style, worked well. I also had an Avent Isis IQ. It worked well too, until the end when the motor started spitting out black dust. Then, not so much...good thing I was done anyway. I did think it was more comfortable though, it had squishy silicone pads on the horns.
I did use those wipes sometimes, although I thought they were too big so I cut them in half to make them last longer. I'm cheap, I fully admit it. ;)
I liked those Medela sterilizing bags too, very handy. You use them multiple times, so the price was worth the convenience for me.
I did get a car adapter for mine, I pumped in the car a lot. While driving. If you don't need to pump like a mad woman, then you can skip that probably. As a side note, the car adapter made the pump more powerful, it was the only time I didn't have my pump going at full strength...
I never had enough milk to actually store, but I've heard that the Lansinoh bags are the best. I've also heard that some glass baby food jars fit on certain pumps so you can pump right into the container. I've never tested that theory though. There are also lots of different kinds of bottles that fit onto some pumps too, so if you store in bottles, you don't necessarily have to be beholden to the bottles that came with the pump.
I did some pump testing for work and tried all the bags and lansinoh ones were hands down the best
Kelly mom has lots of good info specific to pumping.
Bottles. But one and see what bebe likes. Mine did not care which brand.
I mostly EBF, but will pump some also because hubby and the boys want a turn feeding, too. ;)
These are the supplies I used with my boys, and will most likely have again this time around:
Lansinoh breastmilk storage bags (freeze BM flat for easy storage)
Bottles (of your choice)
Bottle drying rack
Small soft sided cooler w/ ice pack