The Food-n-Fun plan was a combination of dining and activities. It had many forms over the few years it was around. Initially it was for 2 meals and you could get anything you wanted (app, entree, desert, no ETOH drink) with a couple of exceptions. It worked for basically all the sit downs that are Disney's. Most times you could pick any 2 meals you wanted. Kids were also not limited to the kids meals on most options.
Activities included things like the trail rides, water craft, fishing excursions, bikes (except surrey's) and parasailing. Price was around $40 per adult per day (or a little less) and kids $13.50 per day. The problem was it was like going to a buffet several times a day. We got it once for 3 days (min at the time) and by the end of 3 days we'd spent about $400, saved about $600 and gained a few pounds. We were miserable and even the kids were refusing desserts.
In another incarnation it gave you a prepaid card where an adult paid $50 per day and you got a credit of $55 per day. This version was food only. It amounted to a 10% discount. You could not combine this with other discounts and with the DDE 20%, it would have costs us a lot more.