The 28mm will be great for those wide views and some architectural shots in city streets - great for shooting from the hip too when you get that unexpected event happening like a clown busker doing something outrageous to one of your friends when you least expect it.
The 50 is also a pretty versatile lens length.
But, gee, when your travelling is when zoom lenses some into their own! I'm sure you'll find the need for a lens longer than 50mm. If you have any zoom lenses I'd take them (but I'd still take the 28!
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My choice would probably be 400ASA film. I got the point of pretty much using 400 for everything towards the end of using the OM-1. It gives you that extra range in dim light, and indoors, etc and 400ASA these days is about as grainy as 100ASA was when I first started in photography
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Another little tip that I used to do with the OM-1, that I really miss on my DSLR: between shots, I would adjust the aperture as small as possible for the conditions (approaching f/22 say) while maintaining a fast enough shutter speed for hand-holding (<1/30s max), and adjust the focus so the DOF was from infinity back to as close to me a possible, so if something happened I could snap a quick photo (even from the hip if necessary). My mates with auto cameras could never understand what I was doing (they thought I was nuts, not taking time to focus!) but I rarely took too many flops!
Have a great time!
Al.