As an illustrator with hopes of becoming a concept artist/character designer, I could legitimately (well, virtually) beg for this and I know other people could too. We Happy Few has such an interesting style to it (that colourful street design oh gosh ♥) that it would be such a shame for the art of it to not be put into a physical reference.
Another thing that's always amazing is in-game items, such as posters, vinyls, weapons etc. I'd love to see something to do with Uncle Jack.
And on the vinyl thing, I've noticed they've become a very popular form of promo/merch for games/film lately (I recently purchased the Octodad 7", and then there's the gorgeous Hotline Miami vinyls, and the Bioshock 2 vinyls from a bit further back...)
Figures are always a way to go too (especially of the player character if he remains anything like the concept one ;D).
I have to agree on watching the prices too; not all of us have money (but I'd happily give it all to this game if I had it to spare).