I'll ditto alot of what others said. Also, does the NICU have a place for parents to store food? Our parent room was small but we could store whatever we wanted as long as we labeled it. You could buy healthy snacks that are in individual portions, like 100 cal packs, instant oatmeal (supply booster!), small boxes of cereal, baby carrots, etc. Bring freezer meals in one or two serving portions, ready to reheat. If she wants a hot cooked meal, maybe throw the meal in a (disosable!) pan ready to thaw and cook. Staples like milk, bread, etc. You can freeze raw cookie dough in "scoops" so she can pop a few cookies in the oven and have fresh, yummy, homemade cookies without any hassle.
Maybe say that every Saturday you are going to come help and clean once the baby is older and that your "payment" is seeing the new baby and holding it if she is comfortable letting you hold the baby. (I am still picky about who holds my 10 weeks old!)
Buy the auntie gifts- cute clothes, but nothing that goes OVER the head. Sleepers that snap, kimono style shirts, etc. This allows all the monitor lines to be out. Soft, washable "hanky babies." Burp cloths- I would tuck one under the girls to catch all the milk and then tuck it next to my baby so he could smell me. Also, take home the laundry from the NICU and wash it so she doesn't have to worry about it.
Disposable cameras, batteries, etc.
Unscented but super mostiurizing lotions because all the handwashing can do a number on your hands! (Mine STILL have no recovered!) Purell too- small bottle for the purse/diaper bag and a bigger one for the house or NICU.
Trashy, light reading. Ask if she wants anything to do with babies.
If they allow portable DVD players in the rooms, some movies.
Buy an MP3 player or iPod and fill it with music for her to listen too or "steal" hers if she already has one. I wish I had used mine but the power died and I never had the time to reload it with songs.
A unpadded ring sling. When he is bigger, you can hold the baby in a ring sling (put the baby in at the bottem so the line can hang out), cuddle, rock and read!
A "baby's first year" calendar. I wish I had had one to record all the NICU mildstones but avoid one that says, "It's month 2! Your baby should..." Hallmark had a nice one I used for my dd that was just pretty girly stickers with generic mildstones (held head up, met grandparents) and a place for a photo every month.
Offer to be the family "go to" person so they don't have to explain everything to everyone ten times over. You could start a blog- I use blogspot.
When you say, "How are you doing?" and she says, "Fine" you might say, "Are you REALLY fine or are you just saying that because you think I want to hear it?" Lol- a friend did this to me and it gave me the freedom to a) laugh and b) tell her what was really going on.
If she has a hobby like scrapbooking, offer to bring her her supplies in the NICU.
The single best gift I got was a huge bag filled with pumping supplies- those "Steam clean" microwave bags, milk storeage bags, lanolin, treats for me, etc. I nearly cried when I got it. Plus, I was lucky enough to have enough tubing and supplies to keep a set at home and a set in his room. This was a LIFESAVER. You might include a small cooler to transport the milk in, sharpies to label everything and a large but pretty diaper bag.
Thank you notecards if she is up to writing them. If not, perhaps offer to write them for her. Kosher? Maybe not but still one less thing for her to do!
Also, steal her away for coffee for awhile, even if it is only to the hospital cafeteria.
Gift cards for resturants, gas, phone, etc.
Good luck and a big congrads to the tiny new addition!