While Lucy is right that there are no services right next to LaGuardia (except for the Courtyard Hotel that is literally across the street), you are only a short cab ride from the Queens Center Mall http://www.shopqueenscenter.com/ the largest mall in the area.

However, do be wary of the traffic going south on the Van Wyck Expressway from LGA to JFK. There are lots of elements that make it a very slow ride - construction, frequent accidents and cars breaking down, traffic merging from other freeways. I would allow plenty of time to get from one airport to the other.

Mark in Los Angeles