I stayed in a yurt on a pumpkin farm, and in October there were fabulously coloured and shaped pumpkins everywhere which was of course delightful. The place is Wowo and in addition to the various yurts also has standard campsites. At reception is a little shop with organic toiletries, snacks, and essential camping food including usually - and this astounded me - vegan marshmallows for the campfire! Wowo was great and I'd certainly recommend it.
This bit of East Sussex was a mystery to me so I just did lots of exploring while down there. Unfortunately a car is pretty essential if you want to do much of this though you can get to most places I mention within a couple of hours by bicycle. On the way down we stopped at The Old Dairy which didn't have much for vegans in the cafe but the shop was an amazingly well-stocked health food shop including Booja Booja ice cream. This was very unexpected indeed for a little place not even on a major road or in a town. Vegans may want to steer clear though because the place is a working bird farm - various free ranging feathered folk as well as large cages with budgies, goldfinches etc. presumably bred for the pet trade.
The Wowo website recommended a pizza place in a nearby village called Forest Row. The pizza place was pricy but had a good ambience and vegan, gluten free pizza bases as an option. Forest Row was the real surprise. I'd never heard of the place and it turned out to be like Hampstead but in the middle of rural East Sussex. In the town square was Macrobiotic Shop - a large, 100% vegan and eco shop the like of which I've not even seen in London. Weird. The place had loads of vegan cakes including tiramisu. We asked the guys working there why Forest Row was like this and he said there is Europe's only Rudolf Steiner college as well as the UK Scientology HQ down the road. I guess that would do it. Just off the town square there was also a decent-sized health food shop called Seasons and behind that an organic fruit & veg shop with some of the prettiest produce I'd ever seen. Organic Stepford. Nice village though. The Forest bit refers to Ashdown Forest which is the location of A.A. Milne's 100 Acre Woods, so that's one of the leading attractions in the area. It's got woods, hills, heathland, the lot. Various bits were used in the Winnie the Pooh books and so are labeled as Pooh Corner, Eeyore's Gloomy Place etc. We visited the actual Pooh Sticks Bridge which is a short walk down a path. It's a big place so again, wheels are recommended.
When we left Wowo, the pull of the coast was irresistible of course, but before Brighton we stopped off in Lewes which was a first for me. I mostly knew it's reputation for dangerous antics on Bonfire Night. It turned out to be a great little town with a pretty high street on a hill with views, a castle, lots of cool old buildings and a crucial health food shop at the bottom with vegan cornettos.
The rest of the time in East Sussex was spent visiting National Trust properties which are enjoyable but not generally known for catering that is either affordable or vegan-friendly. As just one example I can recommend Standen.