I’ve recently been using an app for iOS called fooducate. It let’s you scan food and helps determine how healthy it is. I realize this might not be feasible within your scope, but if a cart could help you eat better I think that would be interesting. Potentially segmenting the cart into different food groups or something. If people didn’t buy any fruits and all carbs they’d be able to see it.
Just a thought.
The germ thing also seems pretty interesting to explore as far as antimicrobial materials go and such.
good luck!