If you had unlimited gas but no passport, and wanted to take a circuitous trip around the U.S. starting and ending in San Diego -- making sure to hit the other corners of the continental U.S., Florida, Maine & Washington -- what could be a route you would take if you started east and only stayed on 10 or fewer one/two-digit interstates?
I-8 -> I-10 -> I-95 -> I-76 -> I-81 -> I-78 -> I-95 -> I-90 -> I-5 is one option. You must take into consideration that I-95 is not a through route in New Jersey to get this right.