Hi , I'm James DVM MRCVS and would like to help you with your problem
Sorry to hear about Squeaky but I would not place the Thunder storm as something which might have resulted in him being off his food and vomiting .
On the other hand there are many things which might still cause such symptoms to develop , such as various viral or bacterial diseases which he might have gotten from eating something he shouldn't have . It could be as well some poison like material which he might have eaten and which could have gotten him sick.
What is most important is to have him checked out for what is the real cause of his disease as well as treat him towards his symptoms , meaning , making sure he is well hydrated and if not attending to him so he will be by administering fluids , if possible orally but better advised , via the vein.
As he is but a young lad , he can easily get dehydrated which will be at this point of time the most life threatening of all his symptoms. I would not advise to dwell on it over the weekend but rather seek the help of your vet which will have an OHH service available..
I sorry about the severity of my words , but fro my experience , young cats require intimidate attention (like young kids) and so I don't advise any home made therapy which could serve as time wasted.
If you have any more questions you wish to ask , do let me know .
I wish you all the best (let me know how you get on).