No effort needed -- MiniVend does this automatically.
Every user session that is started by MiniVend automatically creates a variable set for the user. As long as the user session is maintained, and does not expire, any variables you set on a form will be ``remembered'' in future sessions.
Don't use the prefix mv_ for your own variables -- MiniVend treats these specially and they may not behave as you wish. Use the mv_ variables only as they are documented.
Also, because you can set so many variables, MiniVend does not unset variables it does not find on the current form. That means you can't expect a checkbox to become unchecked unless you explicitly reset it.