We feed our cats Whiskas pouches. They’ll eat anything though, to be honest. Not sure it’s the ‘best’ food for them, but they wolf it down. They also have crunchy biscuits to give them something to crunch on, but make sure they have plenty of water to go with the biscuits.
As for litter trays, get one with a lid – it makes a massive difference to the stink and also how far they can fling the litter while trying to dig a hole for it.
Type of litter; I prefer the non clumping stuff. Can’t remember what we used to buy, but something from Pets at Home worked well and was cheap for a large 10L bag.
Get a scratching post or two.