Haven't used one in years.
Memory sticks are the best freebie - hands down. I still use several I got from BETT including the nifty credit card shaped one from three years ago.
Mugs are OK but most of us have too many of the things anyway. Food is good, if transient!
Stationery is definitely useful
Cuddly toy? - On my shelf I have an HP teddy (courtesy of @bossman) and my lovely Ruckus dog :)
Personally love the moleskine notebooks that Google, Adobe and Microsoft have all been handing out. Have several of each and currently using my MS Technet one for notes :D.
Mugs are a pain to transport, pens and other stationary is great as are (decent sized!) memory sticks. Too many memory sticks I pick up are stupidly small sizes and just end up in the bin now :( Food and free drinks are always good and encourage me to visit the stand ;)
Have got a couple of handcrank LED torches which are useful as freebies before. They stay in my bag for emergencies :).
Best BETT freebie was actually Beer :)
Get yourself one of those cutters or printers and knock out personalised pens / key rings with your name and number as well! Defo keepers.
Apart from edugeek freebies, the one that has lasted longest is the Capita ice scraper. It has proved to be more effective than any of the others we have had and remains in my car. Not that we use SIMS in my school :)
edit: I think that prize might break my anonymity from certain vendors so I wont mention it.
but before that Encarta 2000 (I think. it was 2000 might have been 99... it was for writing something amusing in very early demo of the technology that was to become sharepoint)
Wrist Supports - these are as much of a holy grail as Mugs. Stress squeezers with a decent memory-foam type action - not just cheap foam balls but the ones that take a few moments to recover their shape. Or better still the ones with actual gel in. Lanyards. I LOVE Lanyards. USB Sticks are good but promo ones tend to be really small capacity and I CBA with those. Lego is instant-WIN as are those 'office supplies construction kits'. I'm addicted to whiteboards and whiteboard markers. And magnets. LOVE magnets. Am trying to get @ibpalle to arrange a little SIT roadtrip to BETT this year but I think we're too late (also I'm pretty sure they might make me wear Smoothwall branded clothing so my ability to anonymously sneak about and nab freebies would be severely curtailed). Desktop organisation like pen pots or organisers are good. I love mugs too but I have a thing about cylindrical mugs. I can't bear to drink out of them and they end up used as pen pots. I have to drink out of 'conical' mugs - you know the ones that taper gently towards the bottom. It's a weird idiosyncrasy I have.
Those thermos cups are great freebies too although they leak. I recently bought @ibpalle this awesome drinkpod thing that is sort of a flask but not - it holds a cupful and you just unscrew the lid and drink out of it rather than have to faff with pouring into the lid-cup. Best of both worlds IMO and no leakage. Probably way beyond the freebie budget though but I'm pretty sure the company that makes them do custom ones. I also really like those little tins of sugarfree mints and the grapefruit flavoured ones are lovely too.
Insulated thermos mugs are always good for people who have to travel a long distance to work, still got the one RM gave me last year! As are 8GB or higher USB Sticks, still got a couple left from last year which we have build disks or killdisk on.
I really liked those notebook notebook's Lenovo gave a way a couple of years back. Very clever I thought.