Sheet Metal Design

Is there any specfic mathematical way to calculate that thickness ?

The collective weight of objects inside the vending machine equals to 100kg.

If you are a Solidworks user you should be able to use the Xpress simulation add in to test it if you model it as a part. I usually lean on my experience in metal manufacturing to make a judgement based of what I know the material to be capable of. If I find a scenario where I'm uncertain if the material will be sufficient I'll model whatever it is as a part and run a simulation express on it.