What is wrong with my kitten?

The mustard vomit it a mixture of something liquidy he drank and bial in his stomach. I'm not sure what's wrong with him, but I've seen it before. My friend had a kitten and she was in that exact state. Two nights later she passed away. (but this cat was highly inbred and the runt of the litter) give her a can of wet food every day because she might be underweight. You don't mention how long you've had your kitten. If you just got it, I highly recommend taking it to the vet, but I understand with your money troubles it would be tough. I'm sorry to say that it might be unavoidable, but it's only a suggestion. Good luck and I hope your kitten will be okay!