On my colonoscopy diet days I always have Nigella's marmite spaghetti, you just melt some butter in a pan and add marmite, some of the pasta water and parmesan to make sauce.
And you're allowed smooth peanut butter so I have noodles with peanut butter, soy sauce, sesame oil, lime juice, and an egg scrambled in, it's quite filling.
Make use of the few types of fruit/veg you are allowed, my list says tinned peaches, cauliflower, sweet potato, melon, ripe banana so I have those.
Cream of tomato soup is allowed and the acidity is very welcome.
Take the opportunity to get some fancy shortbread or whatever low fibre junky thing you don't ever buy for yourself, you need a treat.
Going into different territory here but if you have the prep drink which I'm assuming you do - it's incredibly sweet so it's not helpful really to have a variety of sweet drinks around for your liquid only day (lemonade etc). Have some savoury or sour stuff like lemon juice to add to water, chamomile tea, miso soup, stuff like that and just have just one sugary thing for calories, like lucozade (not red).
Sudocrem and moist toilet paper for the arse.