There are a lot of things you need to do that can't be done in hospital - like getting your discharge letter to your GP, like getting them to complete the form to send off for exemption from prescription charges, like advising the DVLA that you are now T1 - you have to do that yourself (assuming you hold a driving licence of course) but easy enough to do online now I think.
Adequate supplies is the main one immediately (brand new glucometers for fingerprick blood testing, you'll be doing a lot of that! only come with 10 strips in the box and that's nowhere near enough to be going along with) and the knowledge of what to do with the used needles until you get a sharps bin of your own, plus what arrangements you need to make to dispose of it when it's full. In some places you can return them to your pharmacy but in others you have to register with the council and they arrange to collect them from your house after you ring them to ask them to each time.
That phone number is important - your initial doses of insulin will change A Lot once you get back home and you're starting to lead a normal life, and will need a lot of adjustment both to begin with and on an ongoing basis, the only difference being they probably won't be such drastic changes individually as time goes on.
Just take a very deep breath cos it's a huge learning curve - but don't ever think you need to know everything immediately cos you don't. And when you don't know or are in any doubt about what to do when - just ask! Ask, ask, ask - never stop asking! The most important thing about this advice is that there are NO stupid questions where this is concerned - they are all important cos you need to know the answers and that's that.
This forum is open 24/7 too so even if it's late at night and a weekend - someone's most likely going to be browsing and we collectively have thousands of years experience of living with it and have probably had a similar experience unless you're an astronaut by trade!
Good luck - and do let us know how you are doing, even if you have no questions!