Dsd gets following from her prep:
Classes streamed to ability - no more than 5-10 students in each subject at her set.
3 languages - French, Spanish, Mandarin. Option to take Latin or Ancient Greek but I wanted languages she could use.
Music lessons - not a priority for us but dsd finds singing in the choir and playing piano relaxing so we encourage her.
Breakfast lunch included - dinner can be bought as part of dinner club. Once a quarter all kids and parents are invited to a family dinner.
Uniform free (dsd is on academic sponsorship)
Discounted kumon
Free 11 plus prep.
Trips to places we'd probably never be able to take her like Galapagos and the Amazon for older kids. Dsd has been to Paris this year as part of French class, Seville for Spanish, and they go regularly to UK museums/theatre for English/Sciences, was offered a class trip to Beijing for mandarin but we declined this year. We pay for the trips of course but the costs are fairly reasonable.
Dozens and dozens of social activities on weekends - this is the best part. Brownies, bake sales, choirs, play dates. We donate a bit of money, have a good time, and make a decent support group of similar parents. The other parents from dd's classes are so friendly and as only 5-10 max in each of her classes we can plan birthdays etc with a minimum of fuss.