Best memory stickWatch
I assume you will be transferring small files such as word, powerpoint etc so size and speed won't matter too much. I don't think many places sell 1GB or 2GB sticks anymore, so go for a 4GB or 8GB.
Argos always has great deals on memory sticks, but you can also take a look on eBay.
Don't buy anything less than 16GB. Try and get 32GB if possible as the extra space is always useful.
If your PC/Laptop supports USB 3.0 (your PC/Laptop USB port will be blue), don't forget to buy the USB 3.0 version. It will still work with ports that are not USB 3.0
Also, as @bob0079 mentioned, sign up for OneDrive, Google Drive or DropBox and use that as either a primary means of storage for your files, or a secondary one. Download the app for your computer so you don't have to keep logging into the browser, and so that you can easily keep your memory stick and drive in sync.
Useful? I would appreciate the rep!
Who's going to be using over 16GB for a one year PGCE course, especially if they're only really going to using text documents, PDF files and presentations? It's not worth spending the money when you can get an 8GB or 16GB stick for cheaper.
Also Argos has 16GB for £9.99, and a 32GB for £14.99 (offer) ATM. They even have a pack of three 16GB sticks for £19.99 - thats about £6 each!