Enjoy this time! Passionate love with your novel is a really special thing, but just like any love it will burn fiercely and glow warmly in turns. Sometimes you can't tear yourself away, but other times you'd beg, borrow, and steal just to get something onto the page. I don't mean to discourage you, merely to point out that it probably won't always be like this, and eventually you'll be able to get a breather and reconnect with this strange place known as the outside world and that odd man hanging around who says he's your husband.
I agree with the timer, though I've never had to do that (I'm a very slow writer). I do, however, have an entire drawer in my desk dedicated to snacks. They range from Cheez-Its to dried fruit to dried edamame (awesome source of protein that are munchable like popcorn) to Werther's sugar-free coffee/cinnamon/apple caramel candies (DO NOT try those unless you want an addiction). Make sure at least one or two of your options give you good enough nutrition that you aren't munching on sugar and carbs all day.
My favorite tip is a bit off topic, but with you being in the "marathon writing" stage I think it applies here. Get up and walk around at least once an hour, preferably at least twice. Step away for a moment and stretch, walk, take out the garbage, clean out the dishwasher, say hello to the cat, do some sit-ups, whatever you want. Just make sure you move around. Sitting for hours upon hours in one spot can really damage your joints, make you stiff, and also lead to sedentary habits that give one Writer's Butt (that strange expansion of your hind quarters that comes from long hours at the computer...). Also, doing random little things helps keep your subconscious going, which in turn helps keep your story going in your head.
Congrats on the novel-love, may your writing be fruitful! And welcome to the Bransforums!