Clearly, one of the primary features of these barbecues is their size and portability. Besides the backyard, they are commonly used on the beach, at tailgating parties, camping, on picnics and just about anywhere a car or truck can be driven.    Today's portable grills don't sacrifice performance for portability. Gone are the old style glorified griddles.   New portable barbeques have better construction, sport larger grilling surfaces, higher BTU's, even grilling and unique design.   If you're grilling needs go beyond the backyard - look to a portable grill for quick easy transportation to any destination you have in mind.