try a google search for fresh water tanks/ waste water tanks. I would measure the space to see what you can accommodate on your cart.
Depending on how much water you intend to hold you could rig up a simple setup with a food grade bucket, lid, some pvc pipe and a marine pump. This is what i use on my cart.
That would limit you to 5-7 gallons depending on what you can fit on your cart. you can use any type plastic container to drain your waste water in. IT usually needs to be 15% larger than the size of your fresh water tank. Mine is a 6 gallon waste water tank and a 5 gallon fresh water tank. I tend to carry a 5 gallon plastic carboy with me to use for steam table and emergencies.
Water heaters can be found pretty easily. Tankless propane heaters can be found between 100-150 dollars and sufficient for a 40-50psi marine style water pump. I bought my last two on ebay for approximately 120$.
If you need any of these things in a hurry check if you have any local marine or RV supply stores, they may carry what you are looking for, but you will pay more for what they have. They also will not be familiar with what you are using it for so you need to know how much space you can afford and where you can house things like a propane water heater or how much PSI your pump puts out.
Walmart, lowes, home depot etc will typically not carry the type pumps, heaters or tanks you need.
you are going to have to provide something for people to help with a schematic. There is no "single quick fix" in my opinion for most of these jobs you have to be able to improvise what you need and how to make it work with the space you have. Most of the plumbing pieces (aside from the tanks,pumps, and water heaters) can be acquired from any local hardware store. I'd just be sure to speaks with someone that the pipe you are using is correct for what you need the water for.
Also i think there is a separate forum for carts, that you might find more responsive to your needs...
best of luck