You did not indicate the purchase cost to the student. But if the swipes are limited to 10 swipes a week for 10 weeks and the cost is $1,200 then when the student purchases the meal plan at the semester start you have cash db $1,200 and cr Unearned Rev for $1,200. If the student uses 7 swipes a week and as a result forfeits 3 swipes a week, then each time they swiped their card you db Unearned Rev for $12 and cr Sales Revenue for $12. At the end of each week you db Unearned revenue of $36 and cr Forfeiture Revenue of $36 because you earned it through their failure to use the swipes. The posted retail value of each meal, such as $8 for a burger i meaningless in the sense that the student lost a full swipe at that time.
I guess on an $8 meal you could db Unearned Rev $12 and cr $8 Meal Revenue and $4 to Forfeiture Rev to parse our the two. But ultimately you earned the value of 1 swipe and each swipe carries a value = to the cost of the initial total swipe package / # swipes.
Here is to hoping I'm not missing anything! But that treatment seems to be appropriate. You are really moving from using a dollar denominated retail value to manage the declining value to an alternative valuation of what a swipe is worth.