Indeed there are other non league matches in Sussex however I only had the County First division at my pissed up disposal last night and also I can't personally guarantee you can drink pitchside at Eastbourne Borough. (And Eastbourne Town is cheaper and will have a better atmosphere)
Generally speaking you can have a pint pitchside this sat at:
AFC Uckfield
Crawley Down
East Preston
Eastbourne Town
Hassocks
Horsham YMCA
Littlehampton
Loxwood
PEACEHAVEN & TELSCOMBE
Worthing Utd
Enjoy