Had a sticky beef Po' Boy (essentially like a posh-ish kebab/sub) yesterday on the Island Like No Other, with cajun fries - this was from one of the pop up Mardi Gras food stalls which are not Aramark run. £14.50 in total for both, and it was genuinely decent. Pint of Camden Pale was £6.75 but had to be done because sunshine innit.
Similarly, at Fright Nights I bought food on two occasions from the Ghost Train Smokehouse near the teacups, again, external, and was very good indeed.
So basically, just go when there are pop up traders xoxo