In the early days: snacks, and bottles of water - I had 'feeding stations' one upstairs, one downstairs so I didn't have to traipse around the place with a yelling baby. I was absolutely ravenous at first, so the snacks were definitely required, especially at night - dried apricots, muesli bars, bananas, chocolate. Bin also useful for all the rubbish from the snacks! Was DHs job to replenish the stocks.
I also had a radio/ mp3 player/ laptop to hand for the night feeds, plus a small reading light - to help keep me awake, and to help me see the latch in the early days when neither of us knew what we were doing.
I just used to use ordinary pillows to raise DS up to the right height to make feeding easy for both of us.
Also useful - DS was born in the winter and I used to get really cold doing the night feeds (am a pretty cold person anyway) so had a big shawl to wrap up in and lots of fleeces to hand.
Tops that undo down the front/ nursing nighties - I got cold (as mentioned) plus confused at night, so something I could unbutton was easier than trying to raise and lower different layer of clothes to get a boob out while staying warm (old soft men's cotton shirts worked well for me).
Nursing bras for night - more comfy to have some support and something to hold the breast pads in if you leak at night (a waterproof mattress protector was also useful for this, but has also been useful since when DS has vomited/ spat calpol everywhere/ etc).
Lansinoh!