I have spent a total of nearly 20 months in hospital over the last 6 years, and have become very accustomed to the food! My favourite is the cottage pie (usually served with mashed root veg and extra gravy) and the roast dinners (particularly pork with apple sauce). I'd also recommend the tuna mayo jacket potato or sandwich - but be sure to write a polite message on the menu asking for a couple of packets of butter, as for some reason, they seem to think that tuna mayo sarnies don't need any!
Most meals require a sprinkling of salt and at least 3 sachets of black pepper, but it's the sort of plain, simple, comfort food that you need when you're not feeling 100%. If you're going to be in for a while, it's worth building up a little store of condiments (salt, pepper, butter, mayo, ketchup, vinegar etc.) as most hospital food is fairly bland and you may find, depending on which ward you're on (thinking of Renal in particular here), they may not let you have salt, for example. Not a lot they can do if you have your own though! 
Once you've made friends with the Nurses and HCAs (and if you ask very nicely!), they will often happily rustle up something simple for you (beans on toast, tomato soup etc.) if you're hungry outside of meal times, or if there's nothing you fancy on the menu (and if they have time!), although I haven't asked for any "extras" like this since Covid hit, so I don't know if it's possible at the moment. Failing that, there's nearly always biscuits!
Never, ever, no matter what, even if there is no food left in the entire hospital and you are so hungry you could eat your own leg, should you order the faggots. I swear they're made of cat food. At least, that's exactly what they smell of.
(not envy)