My advice is that Ikea is not essential. Dd1 told me it was. If you go to the Southampton one, you can see if my will to live is still hanging about because I lost it somewhere before the first corner.
And we hardly bought anything, certainly nothing we couldn't get for same price elsewhere.
Firstly, you need to find out what they want.
Then remove the really expensive "essentials" that aren't essential, but they're trying to slip under the guise of "desperately needed" while you're buying other things in the hope you will be both gullible and not too observant.
You'll be left with things like bedding, crockery/cutlery (getting for 2 is fine - the standard thing if they have lots of friends round is they ask them to bring that). Fairy lights are apparently an essential, although quite a cheap one, so you can let that go. I went for battery ones as less likely to burn the place down.
On the subject of burning the place down, you'll probably find some things not allowed (candles is the obvious one, but things like rice cookers/slow cookers even kettles in some places aren't allowed)
However a multi-socket is a good idea because unless the room was built recently it may well be restricted to one light for a bedside light and one under the desk. They may have restrictions to no of sockets allowed from any one multi-socket (dd's was 5, I think)
Pins for the noticeboard is also something that is cheap and keeps them happy.
Don't forget they may need some things for study too.
And buy them an advent calendar before they go. It saves feeling guilty and paying more for postage than the calendar is worth. I may or may not speak from experience there.
If they do send Christmas cards (or think they might) a packet or two isn't a bad idea.
I did a first aid kit for my dramatic one, so she didn't have an excuse to phone up at 2am needing a plaster. She did phone up at 3:30am to tell me she'd been sick once though...
Plasters, pain killers, elastic bandage, cream. I didn't put burn gel in, which was a pity because that was the one first aid thing she needed.
I also provided her with enough sanitary products to see through the first term at any rate.
My girls took a bug catcher.
And don't forget when they go in that sunny day in September, that they'll be there until the cold days in December. It might even snow. So make sure they have gloves etc.