I recommend a 1GB minimum, i picked up this PNY 2GB usb flash drive at my local tesco today for only £1, yes you heard me correct £1!
PS. my first instructable so sorry if im unclear on the steps
Step 1: Lets Get Started
Go to My Computer;
Right click on your usb stick;
Select format - THIS WILL ERASE ALL DATA ON THE STICK SO BEWARE I AM NOT HELD RESPONSIBLE FOR ANY FAMILY PHOTOS OR THAT DOCUMENT YOU HAVE BEEN WORKING ON FOR THE PAST WEEK BEING ACCIDENTALLY DELETED, I SUGGEST YOU BACKUP YOUR DATA!! (copy to your hard drive)
Now do a quick format on the default settings and label your drive - ie: Toms usb apps or Dave's apps - you get the idea;
click start and wait for the format to finish, When this is done go to the next step.