Is it safe to store muriatic acid, hydrogen peroxide and acetone?
You don't need to take any special precautions when storing these chemicals together compared to how you would store them individually. They should all preferably be stored in their original, properly labeled containers with properly fitting lids.  

Regarding your concern for hydrogen gas forming from the HCl fumes, that is simply not a reaction that will take place from only the compounds you've listed, or in combination with anything else you would typically find in a utility or storage shed. You will want to avoid breathing HCl fumes while working with it of course, but as far as a storage concern even this will not be an issue for you.  

I commend your extreme caution here in general, although your fears of the acetone igniting from sitting in a hot shed are unwarranted. The flash point of a compound is the lowest temperature at which it can be ignited with an ignition source, like a spark. This is commonly confused with the autoignition temperature, which is the lowest temperature at which a compound can spontaneously combust without an ignition source. So, while you really don't want your acetone near a flame or spark source at any temperature, it's autoignition temperature is $\pu{465^oC}$ and so you don't have to worry about it igniting just from sitting in a hot shed.