Get Your Cat Care Questions Answered By Cat Vets ASAP
I'm sorry to hear your cat isn't feeling well. It may be difficult to treat at home if he/she continues to not be able to hold anything down. However, you can try, as long as he/she isn't too lethargic, unresponsive, or painful. It may just be some stomach upset, but if not clearing up soon, you'll want some diagnostics from your vet to rule out problems like infections, liver or kidney issues, or hyperthyroidism, to name just a few.
Wait at least 12 hours before feeding, a bit longer if still vomiting. Then you can try very very small amounts of a bland food, like Gerber baby food (chicken or turkey flavors are good) or boiled chicken. Just about a tsp or bit less.
If able to hold down, try again in an hour this same amt. If doing ok, do this for a few hrs, then about 1/2 a meal amount for his next meal time.
If doing ok, keep on bland diet for a couple of days, the gradually switch back to normal food. If not able to hold down anything down, he/she'll need a vet visit, as injectable medications will be called for. Also, make sure he/she's drinking water the entire time so as not to dehydrate, and keep him/her indoors while recuperating.
Best of luck, hope your cat is better in no time!