When dh was young, he and his family stayed with some friends, and on the last day, the hostess asked dMIL what the boys' favourite meal was - and she said mince and potatoes - meaning savoury mince with plenty of onion, carrot etc in it, and good mashed potatoes.
The hostess had never made anything like this before (not even a shepherds/cottage pie) so just put raw mince in a pan with some water and boiled it until it was cooked, and served it with boiled potatoes. Apparently it was absolutely vile, and dBIL was sick in the car on the way home.
One of my favourite stand-bys with visiting children is chicken tortillas - warm tortillas, chargrilled chicken cut into strips, grated cheese, plenty of salad, and some guacamole, sour cream and mayo - all in bowls on the table so they can put in whatever they want. It's delicious, and I do it for the whole family sometimes, too.
Otherwise, burgers are a good choice - make your own with good mince and serve with some salad and wedges, in a wholemeal or 50/50 bread roll. Pizza is good - especially if you have the energy and motivation to set out lots of different toppings and let them create their own pizzas on either bought bases or home made ones.
Oven roasted chicken drumsticks, with salad and crusty bread or potato wedges is also pretty popular (and easy).
Re. celery in a vase - my mum used to put it in a jug to serve it - not that different, I suppose.