Upgrades in the Food Truck work a little differently compared to the rest of the game. You'll have three options:

 

1. The New Food option, as seen above, will add a new food or station to your game to help you earn more Truck Bucks and climb the leaderboard.

 

2. Food Upgrades are chosen at random, and will only be applied to currently owned foods. You can see the percentage chance by tapping on the small blue i.

 

3. Station Upgrades are chosen at random, and will only be applied to currently owned stations. You can see the percentage chance by tapping on the small blue i.