You have to go to the vet asap. If you could wait until Wednesday, he wouldn't be sick, right? As the other person said, you can also take a check with you that is dated for Wednesday and give it to them and see if they will examine him. If there are other people in the waiting room, maybe they will offer to help you.
No matter what, you have to just go. He could die of dehydration otherwise. You will be able to tell if he is seriously dehydrated by pinching the fur on the back of his neck. In a healthy cat, his fur should immediately relax when you let go. In a severely dehydrated cat it will stay rigid and take a longer time to go back down.
The only other thing you could do, if you cannot go to the vet, would be to take him to an animal shelter, and beg the the people there to help you give him subcutaneous fluids and offer to pay whatever you can afford. You will have to put him in a carrier and cover the carrier with a towel.
Wherever you go, you have to cry and beg people for help. If you go to the vet, just start crying and ask if the vet techs could just look at him so you would know what he needs to make it through until Wednesday.
The problem is that none of us can tell you what to do because we don't know if he has a temperature or has ingested something toxic. Is his nose warm? Most often a cat's nose is cold and wet.
At the very least you need to find out if he has a temperature. That will help you determine if he has a virus or infection versus a physical injury. If it is a virus or infection you should be able to beg some pills from a shelter. You would need to give him those (usually clavamox) and you would need to force feed him A/D wet food with a plastic syringe from the vet's office or from the shelter.
No matter what, you need someone to look at him and you need to do it right away. Cats die very quickly from dehydration. It would be completely ridiculous if your cat died simply because he had a fever and could not get to the vet for diagnosis in time.
