If the terms of your event allow it, it is nice to be able to offer those who are really keen the chance to get their own Go set and book.
However this takes a lot of effort to organise.
Firstly you will need a stock of sets and books. Pentangle will usually supply these on a sale or return basis but there might be a cost for delivery or return. Also the stock is something else to have to carry to your stall, often from a distant car park or from the station. A venue that has convenient on-site parking is a rarity, and often unloading is not easy.
If you do decide to sell, then the best Go sets are 9x9 ones or the 13x13 ones with 9x9 on the back. The two types are the one with Go mats, which are cheaper and lighter, and the ones with plywood boards in pizza boxes, which are nicer to play on. You should avoid 19x19 sets as this would be a big commitment for a student to make and, as you know, small boards are better to learn on.
You may also supply a beginners book at a reasonable price, such as that by Charles Matthews or that by Neil Moffatt (both British Go players), but do not expect to sell as many as the sets.
The BGA can supply you with a supply of such sets and books to sell, heavily discounted and on a sale or return basis. You should contact the bookseller  in good time to discuss your requirements.
Also you will need appropriate amounts of change and somewhere to keep it. You will find a lot of people will not have cash on them, but at least you can show them what they can buy and direct them to Pentangle to buy on line.