Reddit mentions of OP/TECH USA 6701062 SLR Wrist Strap (Black)

I'd definitely agree on a spare battery, 2 MIGHT be more than you need, but if you're going to be out shooting all day it probably wouldn't hurt. I haven't needed more than 2 for my EM10m2. That 17mm isn't a great lens, but it's still a step up from the kit lens at 17mm in both aperture (about a stop) and image quality. As far as buying another prime, I would hold off at this point unless you get a lot of time playing with the camera before you leave and really notice the limitations where you like to shoot. The Panasonic 25mm f/1.7 can be had for pretty cheap, so if you do think you want to snag a used one for your trip you can probably resell it for not much less than you paid if you find you don't like it.
 
I have found that a wrist strap is a great help when out shooting, but it's a bit of a pain when you're just walking around being touristy. I have this wrist strap paired with this neck strap; I do think I need to get an extender for cross-body wear with the neck strap, but otherwise the quick-change-ability has been REALLY nice.

Not sure what you mean by "simple", but OPTech does some very nice ones. You can also buy the end bits separately and transfer the strap among several cameras.

Have a Gordy's but I prefer the Optech wrist strap http://www.amazon.com/gp/product/B00137NMMW/ref=wms_ohs_product

Feels nicer on the wrist; when I don't want it flapping around on a tripod it's a quick disconnect. Gordy's is prettier though

I've been using this for a few months and love it. When I need to shoot, I unhook the strap and put it in my pocket. Definitely stays out of the way much better than a traditional strap.

I find that this http://www.amazon.com/gp/product/B003T0EYVE/ref=wms_ohs_product?ie=UTF8&psc=1 is very comfortable and keeps the camera ready but most of the time I use the same connector on the camera and attach this http://www.amazon.com/gp/product/B00137NMMW/ref=wms_ohs_product?ie=UTF8&psc=1 You can switch back and forth easily. I use the Lowepro event messenger 250 to carry all and can fit my Nikon D7100 w/ 18-200 lens plus another lens or speedlite.

If I'm shooting an event for work or doing a lot of out and about shooting, I'll throw my 60D on my Blackrapid (RS4) strap. If I'm doing some light shooting or even if I don't feel like wearing the Blackrapid, I use an Optech wrist strap here. I like the setup because I can also just easily unclip the wrist strap when not in use.