Hmm, good one.
My bathroom door is flimsy, too. We live in a double-wide trailer, and have two bathrooms; a big one in the master bedroom, and a little one out by the front room. We don't use the master bath (storage), so in addition to having a flimsy door (and walls), I wouldn't have much space, either.
Overkill, I like the towel-armor idea. What about the shower curtain as well? In addition to the towels protecting individual body parts, one could drape the shower curtain around, cape-style, or even cloak-style (covering the head, too). It might, however, just be in the way, or could get caught on something, zombie grabs it, etc. However, depending on which zombie camp you hail from, the vinyl cloak could protect you from other hazards, namely biological (flying zombie-slobber, blood, etc.

).
Besides the plunger handle, one could employ the shower curtain rod. Some folks have two, one for the plastic curtain and one for the frilly lace pretty cover-up curtain. We just have the one plain old plastic one. The curtain rod is a bit flimsy, but if the plastic ends were taken off and the ends of the rod mashed to a point or an edge, it could be used as a stabbing weapon. Making it so would, of course, take time, though.
Also, every bathroom has a toilet, and although I've seen plastic ones in trailers and such, most toilets are porcelain (?) and hard. The lid to the tank would make a good, albeit short-range bludgeon. I'm not much on bludgeoning weapons myself, for zombies, anyway, but if it's all ya got...
Also, beneath the sink is the plumbing, often PVC, but sometimes copper. Not super-strong, but again, can be mashed into a stabbing device. We have one of them shelf units that sit over the top of the toilet, you know? I mean, its legs stand on the floor, but the shelves themselves kinda straddle the tank, and are above it. Its main leg members are of surprisingly strong metal. Maybe some potential there.
My own plan would be to wrap up in towels, per Overkill's idea, then cover up with the shower curtain, grab the tank lid, and make a mad dash out the door, try to get through and past them, to some other part of the house, or outside.
Plans look good on paper. Making them work in real life is a horse of a different color.
I know some of you have flares and a handgun in a ziplock bag in the tank but lets pretend were in a normal house
I don't, but that's a good idea!
