As a second option, I set up six columns, one for each truck. In each column, I start off with one slot, leaving room for more. Turned vertically, it would look like so:
This way, if something is known (such as the hot dog truck getting Y in the first rule), I just write Y under the appropriate column. Then, for numbers rules (like the second one), I can draw as many spaces as I need an close off the column. So, in my sketch, I'd have two spaces in the falafel column, and close it off like so:
F: _ _|
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