Island Sub and Burger   Who knew you can get a decent Cuban sandwich in Manoa? This little joint serves a hit parade of well-crafted sandwiches messy meatball subs, pastrami Reubens, cheesy burgers, you name it. This used to be Bonacasa's. A Chinese family bought it, kept the menu, and the hoagie torch continues to burn.  Manoa Marketplace, 2752 Woodlawn Drive. 988-2685. 10 a.m.-8 p.m. daily. MC, VS. No checks. $.