I like British Airways - I signed up for their milage program and I've already got enough for a free flight back to the US!
Try not to worry about leaving your things behind. When I first came over, I had 3 huge bags. When I go back to the states I try to take 1 big bag and stuff another huge duffle bag inside of it (duffle's are good cause they can fold up well). Then I stuff both with as much as I can and head back to the UK with 2 more bags.
It's taken me about 3 trips back to the US to get everything I wanted over here. But bare in mind, the flats here don't have a lot of storage. And if you're living in dorms, they have even less storage (next to none).
Things I would suggest to bring - any type of medication/toiletries you're fond of (ie cold meds, Tylenol, advil, chapstick, makeup etc.) They have meds here, of course, but I don't like any of the cold medications here - I always seem to go through 3 boxes of theirs to get the same effect as a single box of tylenol cold has back home. And the majority of freshers get sick when they first move here... and then again after xmas break. Airborne is good stuff too.
I shipped my printer over here so I stock up on printer ink everytime I'm in the states. There is a Staples in Glasgow, but it can be expensive. Pens & highlighters are also worth stocking up on. Avoid bringing notebooks/notebook paper or binders... the paper here is sized differently and the binders have 2 rings as opposed to the 3 ring ones were accustomed to back home.
A lot of US students will bring back snack food too - peanut butter (just doesn't taste the same here), easy mac, chocolate chip cookies, crystal light & gatorade powder packs.... there are stores where you can find american brands - but can be expensive - and there's also a Costco in Glasgow, but they don't carry all the American brands. So if you like a particular brand of something, and there's room in your suitcase, bring it along for the ride!
And if you're wondering if they have a certain brand of something over here, feel free to ask. If I don't know off hand - I'll find out for you.