Blue-claw crabs, copper catalytic converters, and . . . used cooking oil? Opportunistic thieves have gotten creative in their pursuit of ill-gotten gains in these inflationary times, but used cooking oil does not immediately spring to mind as a high-ticket product worthy of theft. It is a big problem on Long Island and one that visited the East End in recent weeks in a crime wave that hit numerous local and regional restaurants, including Harvest on Fort Pond in Montauk and the Lobster Roll on Napeague.