You are going to be spending a lot of money San Diego Comic con. Like, a lot of money. We really can't stress that enough. You will be flat broke afterwards. Flat broke after having the greatest weekend of your life, and coming back with a massive haul of geeky ephemera and comic books, but broke nonetheless. You need to plan in advance that you actually have enough money to do everything that you want, to pay for all the essentials, and to snag all the cool stuff you've got your eye on. There will probably be times that you have to make tough decisions about what you buy but, well, them's the breaks. Oh and when you are buying things, make sure you're using physical currency. Whilst many of the exhibitors at Comic Con will accept credit and debit cards, you shouldn't just assume they will. There are also those con exclusive pieces of merch that get sold on specific stalls that often will only take cash, so it's best not to get caught out after you've been lining up for hours. There are ATMs in the hall, but sometimes they charge, so just make sure you stock up on bills before you arrive.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/