There is a rest house for truckers that will serve a hearty dinner, its cheap but don't go expecting it to be pristine clean.
You can find private cars going from Murghab to Sary Tash and even to Osh (or vice versa), crossing the village. If you take one of those cars expect to pay about 10 - 20 dollars per person (and maybe double for Osh). Most of the time those cars will be full of people (and full of people in Tajikistan means about 10 people in a small car), so its better if you have your own transportation or you booked something before. But you can ask the locals from the guest houses for a car and maybe they can help you to find a car (which probably will cost you more than usual). Locals know that Karakul is remote and there is no easy transportation, so be ready to bargain their prices for transportation, starting in 100$ just for 150 kilometers.
If you plan to hitchhike make sure you have plenty of time, even in summer. There are no more than 5 - 10 cars passing by Karakul and most of the time they are not going to anywhere far from the village.
You can find basic meals asking in the few guest houses around the village; fried eggs, jam, rice, bread and tea. If you are lucky you can get a soup with some rice and veggies.
You can buy very basic stuff to cook in the local shops of the village, but bear in mind that you will only find potatoes, onions, rice, bread and pasta. The shops are quite hidden between the mud houses, and probably you will have to ask the locals (if you can find them) for the location of the stores (magazin in russian).
There is a a pump at the end of the village (if you are coming from Kyrgyztan), but you should filter the water. If you want to minimize the chances of getting severe diarrhea (no jokes) filter the water you get from pumps all over the Pamirs. There is no bottled water for sale in Karakul, nor in Murghab.
There are several guesthouses for the few travelers who show up every summer. Right in front of the road there is a cheap guesthouse (5 dollars per person per night). You can see the main wall of the white guest house with a "guesthouse" sign written y blue letters.
If you look around the village (it’s quite small) you will find a few more houses where you can sleep.
You can camp near the lake if you wish. Many cyclist and budget travelers camp there with no major issues.