If a girl asks me to carry her bags how should I response?

I mean like heavy suitcases...

she is basicly asking for it in polite way but if I do it I would feel like a wussy bag..

I personally would do it. I'd make sure to also say something like 'man you are so gonna repay me for this... i feel a massage coming on...' or something just to make sure she knows I'm not gonna be her little bitch.
Its just socially good to do so. If she's a chick lugging around a heavy bag and I'm a guy just walking all cool beside her, I look like a complete dick. Not an alpha male, a massive ass with zero social cue reading skills. Plus, its a good chance to show how strong and masculine you are. "Here, let me carry that extremely heavy bag for you"
On the flip side! DO NOT WALK AROUND WITH A PURSE!!!! If your girl just has way to much crap in her bag and she's making you carry it, you're a doofus and are getting owned. Its all about what makes sense and what is real. If she's truly weighed down, you're a champ. If she just wants to not carry her crap, you're a chump

Take the bags off her

Make a face then say why do i have to carry your bags you have bigger arms than me! your starting off your first neg which should hopefully lead into a topic

i completely agree with jovi.

i wouldn't call it a shit test if she honestly needs help with it but don't stand her up just to stand her up. don't believe that myth that you have to be a jerk to get the girls. carry her bags if she honestly needs help with them, but make sure you get in your two cents.

something like "so thats how you view me huh? a bellhop? thanks a lot, hun. " and pick up the bags. (might lead to some role-play later )

or maybe a "geez, high maintenance are we? you know there's a 50 lb weight limit right? "