Their property there as you do to put yours there, in the absence of a specific law to the contrary (something giving priority to parking uses for example).

First come first served in such situations is the typical rule—just like in a picnic area in a park. You do not have the right to remove their property from the public area where it is rightfully placed just as they wouldn’t be permitted to move or tow your car if you got there first. Could you call the cops, force them to move their property, then park there? I guess, but:

Even if the law prioritized cars or prevented garbage cans, and even if the cops wanted to help you, would you then want to leave your car in front of their home having called the cops?