Brighton is quite an edgy place, it's not known as London on Sea for nothing and parts of the town around the lanes are nice as is the Regency Pavilion, my mother lived further along the coast and thought it seedy and was always horrified when I suggested we go there for lunch, but as far as bars and restaurants are concerned the place is awash with them and I think the town is worth a visit, but the beach just no! unless you like stones that is. Swathes of Sussex have stony beaches apart from Camber Sands to the east, very near the historic and picturesque town of Rye lots of nice eateries and coffee shops. West Wittering has good beaches you can walk for miles on, if I was going for a day out that's where I'd go can get there in less than an hour, Chichester is nearby again awash with places to eat. Margate has sand I believe and possibly Hastings, both appear to have their charms, Margate is written about a lot these days as a place to visit and has been regenerated so I imagine you would find lots of places to eat there too.
No idea about Yarmouth but further north in Norfolk there are some super beaches around the North Norfolk Coast, Holkum in particular.........and then if you felt going further afield and west there are the amazing beaches in South Wales Rhossili and Worms Head I think, as lovely as some the spectacular ones in Cornwall and Devon but quieter.
Bournemouth beach has extensive stretches of sand, we go there often, but love the Isle of Purbeck nearby not as commercialised which has a NT area with beach quite unspoilt.
Not a day trip for me, but stayed in Alnwick a few years ago and the beaches up in Northumberland are also outstanding.
Well that's my Neil Oliveresque round up! Hope you and your friends find somewhere nice that suits you all have a good time.
