Here's what they had to say on their blog:
"We’re going to have writers, editors, photographers, illustrators and designers from some of London’s best independent magazines on hand to lend their expertise, but we need more! We’re going to have lots of things that need writing, photographing, drawing and designing, so if you’d like to join in just drop me a line on steve [at] stackmagazines.com and we’ll work out what you can do to help. Or of course you can just drop by on the day and say hello."
Stack, by the way, is a subscription service for the adventurous print lover. Each month they surprise you with a different independent magazine, some of which you may have heard of - Very Nearly Almost, Little White Lies, Oh Comely and Eye for example - and others you won't. Visit stackmagazines.com