We have a single tiny bathroom and we do "dorm baskets". Everybody has one or two baskets for bulky stuff (hair basket, makeup basket, spa basket, toy basket) and they get stored in bedroom closets. We have a nice plant stand I got at a garage sale that doesn't take up much room in the bathroom, and you bring your basket in with you and put it on the stand til you're done.

Is the ceiling high enough to install some wire shelving about 12 inches from the ceiling? We put in some of this shelving and it is great for bulkier items, we also use some clear container store bins for smaller items.

We just redid our very small, only-full-bathroom-in-the-house. Here's what we did:
-Get a hotel-style towel rack for over the toilet. It looks nicer than the standard toilet shelves that stand on the floor. We stack clean towels on it and use the hanging bars for washcloths, hanging small items to dry, etc. Very, very useful. We got our on Amazon and it's been very sturdy and wonderful. Caution: Make sure that you hit studs or use molly bolts, because the weight of stuff can pull it out of the wall. I think it looks classier than the usual toilet things and I can't imagine that a landlord would have an issue with you installing one (it's four little brackets that screw into the wall).
-We actually tore out a (small, useless) linen closet and the teeny sink and used the space for kitchen-sized cabinets (ie, deeper and taller than bathroom sized). The height of the sink is more comfortable for leaning over, brushing teeth, etc (and we're both relatively short). The deep cabinets (some are doors, some are drawers) are very handy. Between the cabinets, losing the closet, and the over-the-toilet shelf, we actually have MORE storage - and it's more useable - than what we had before. Probably not an option for a renter, but just in case.
-If/when we really start feeling pressed for storage, my next plan would be to install a long shelf (like the iKea ones with simple brackets) on the short wall over the door. We could fit several shoebox-sized containers up there and it would be good for out-of-season stuff like sunscreen, extra toothpaste/toothbrushes, etc. Again, landlord would probably not lose their minds over this.
Check out ikea for ideas

you may have to opt for one of those over the toilet storage if there is not enough space to fit a small cart to the side of the sink. if it is a MB you may be able to have the cart outside the bathroom if there is no space in the bathroom. I remember my two biggest pet peeves with my small MB was no place to put the extra roll of TP and no place to store female products in the bathroom.

Target and Walmart likely have some options as does Container Store and Ikea. Here is an example of the toilet etagere.
http://www.target.com/p/fieldcrest-etagere-white/-/A-10939653#?lnk=sc_qi_detailbutton

I live in a tiny old rambler with not very much storage space. I have A LOT of cosmetics and I bought the IKEA Antonius cart with wheels. It's a pain to buy because it's in several pieces...you have to buy the wire or plastic drawers separately, the top (like a countertop) separately. They also sell drawer inserts for the Antonius that are great for cosmetics and little things. I wheel the cart into the closet when I'm done so it's not in the way.

I also have all of the toiletries and medicine arranged in wire locker baskets in the (locked) linen closet. I bought the baskets at Container Store awhile ago.

Good luck!

Container store. IKEA. Target. They all have lots of storage solutions for small spaces.

We just rented a cute little cape cod house, but are now facing the reality of living with very tiny bathrooms (pedestal sinks) without any built in storage except for towel bars and medicine cabinets. Anyone have good suggestions on how to maximize space? Best places for finding storage solutions (on-line or in actual stores)? Any ideas would be greatly appreciated.

Thanks!