Osmand is one of the best in my opinion, but you can also download regional maps for Google Maps and use them off-line. My big beef with the Nexus 7 on a bike is that it's impossible to read the screen in bright daylight, with these old eyes anyway. Plus it's too big for convenience, but with your bar bag maybe that's not a factor. Stopping in the shade to orient yourself sure, that should work fine.

There's a device out now that might be useful with your Nexus 7, and I wonder what the reaction of experienced tourers is. It's a credit card sized mobile hotspot (search for Internet on the Go Mobile Hotspot (3G)) that simply connects up to a pay as you go mobile internet service and beams out wifi. Data is cheap, 500 MB for $10, so it's kind of intriguing to be able to have on-demand internet connection for the tablet, filling in the gap between the tablet's capabilities and a smartphone without needing a mobile or data plan. I haven't tried it so I can't say if it even works, but it's tempting and I wonder if I even need mobile or data for my smartphone if I used this and voip calling.