Em! I echo your sentiment of being absolutely terrified. I just realised in 2 weeks time I'm going to Riga for a week with my OH, and I was soooo looking forward to it, but now that you got me thinking: ... I'm actually scared because I won't be able to know what's in my food, what and where and how much!? ... But I guess, this is where I HAVE to let go of the wall and take a swim out into the open sea. We need to eventually let go of the swimming aid, and see if we can do it on our own.
Though even the thought of going to a restaurant is absolutely terrifying even now. When my OH suggests a night out drinking with mates, or a meal out I always try to find some excuse NOT to. ...and I feel bad doing that too. I feel bad going and I feel bad not going. ... ugh.
And in Plymouth: there will still be shops around. Supermarkets, and such, I mean if you're worried, maybe buy a prepackaged lunch with calories counted for you. A few fruits to carry around with you in your handbag. Just to help you along.
At the end of the day: you need to trust yourself. I know I certainly need to give myself the responsibility too. And you know what? If you can do it (which you proved in Florida that you CAN!), I can do it too. Em, we're in this together! *HUGS!!!*
Daisy: Week 4 looks quite bleak in your choices, and especially with you being vegetarian, it becomes quite a bit more limited. HOWEVER! Week 4 means you can officially have cooked vegetables and cooked fruit - which again - opens it all up to you!
Avoid things cooked in tomato sauce (as this would have lots of added sugar/salt), maybe take a few snacks with you (lots of fruit), take a bottle of passata, and some vegetables (head of a cauliflower that you can pick at, plenty of baby gem lettuces (they don't go off I found

)), brussels sprouts). And a few tins of tuna as well if you eat it. It won't go off not being refrigerated, and will provide you with a good meal if you can't cook things on the spot.
Hope this helps. x