Feliway plug ins tend to help cats relax in new environments.
As for food, it might be an idea to try different varieties, I would try and stay away from high street brands as most of them full of poopies like ash and grain which is not good for cats on a whole. if you try a food with a good protein content and moisture content along with no grain that tends to be better for their indigestion. I give my cats Purizon.
Also try different types of wet foods if kitty is being fussy give him so tuna in sunflower oil or cooked chicken breast. I feed my cats a raw diet which is quite good for them.
Honestly OP it is all try and tested, always buy small tester packs of foods that way you can gage what kitty would prefer.
A good online site that i use which is a fraction of the price that you pay on the high street is Zooplus.co.uk.
They have all different types of not only foods but also litter. i use hooded litter trays which helps with poopy smells and is less messy. You do get a a litter that smells quite nice and clumps really well and will last you quite a few weeks. It is called Biokat which I get from Zooplus, just use the scoop to scoop out the poopies and wee clumps.
I also use woodchip for some of my other cats as cats do like different types of litter.
Also if you do not have one a cat tree or scratching post would be good and will stop kitty from scratching things around the house.
Hope it goes well :)