I'll second and third the BlackRapid straps - I have an older RS-4 and a newer Yeti, and with the Yeti I can carry two gripped camera bodies with flashes and a heavy f/2.8 zoom on one and a fast prime on the other for 6-8 hours before I get tired - and I have RRS plates on my gear, too!
This is the current women's strap from them:
http://www.blackrapid.com/products/kick
Op-Tech is another great strap maker, with all sorts of solutions, but are a bit more pro and more system-oriented. Made in the USA, too. Regardless though, don't carry it around your neck. Besides looking like a tourist, it'll kill your neck after a bit; when I use the manufacturer's strap, I use it over one shoulder.
For a lens, the 17-55 is pretty big and heavy (22.8 oz - about the same as most 18-200 mm) and although it's better image quality than the 18-55, IMHO it's not enough for the weight, especially at WDW. What you're paying for is the f/2.8 maximum aperture, so you can shoot in lower light, but given the age of the T1i you'd get the same low light performance by upgrading your body to the SL1 or similar. For my money, I'd get the 17-85 mm. It's 16.8 oz, so not nearly as heavy, it's less expensive, and the zoom range is more usable, and it's also very sharp. I use the Nikon version (a 16-85) as my walk-around lens, really enjoy it, and the Canon is just as good as the Nikkor.
But to be honest, you already own the lens I'd recommend for walk-around at WDW: the 18-55. Just because it's the cheap kit lens, don't knock it too much, it's quite sharp, and with your older body its few optical flaws are pretty much invisible. For a second, a fast 35/40/50 mm lens to cover your indoors/low light needs ... which you also already own. 35 is more useful than 50 on a crop sensor, but they both do the job.
