you guys are hysterical.... if it was me, I wouldn't dare... not with your suggestions. The thing is, if you go all out surprising romantic, you will look like a creep. If you call her ma'am, you will look like a creep. If you bring in a fish sandwich to the store, you guessed it... creep.
Just go in, be nonchalant. It seems as though you've already caught her eye because she's had her friend ask you about her. That was your shoe in. Next time you go there and she is there, hover around the fish stuff and when she asks you anything like if you need help or whatever, start a small conversation.... that will lead you to asking her to give you a call or ask if you can call her. And go from there. Don't go in with the intention of asking her out on a date.... she may want to get to know you better through phone conversations first. Take it slow... there is no rush.
Just stop going in there every other day for nothing too, that looks creepy.