I did this years ago to fund my college existence, quite succesfully.
I applied to the council for available pitches and hired my fully kitted out van from a large hot dog van company who had older vans that were not being used. I turned over around 30 burgers and 50 hot dogs per night, making around �1.50 on each one. Chips cost �1 per bag and made me 74p and soft drinks made around 30p per can gross profit.
I bought stock in bulk from wholesalers, saving loads of money. The only time it came a bit unstuck was when I sub contracted the van out and the guy was buying his own stock and selling that instead of mine!!!
Regarding insurance, etc, I had a basic food hygiene certificate, commercial vehicle insurance policy, health and safety inspection (local authority) and public liability policy. I took out the PL insurance with Towergate insurance.
Hope that helps a bit, get the right pitch near a night club or taxi rank and yuor laughing all the way to the bank!
One last tip, do not ever wear your best clothes as you will ruin them, they end up stinking of stale frying oil and means your other half will probably come nowhere near you after a shift until you have changed, showered and put your work clothes outside!!! lol
good luck