Which lens to get for trip to Alaska?

I have a Nikon D5000 and bought a Nikon 50-300mm for my trip to Alaska. I have an 18-55, but wanting a wide angle lens. I'm thinking about renting a Tamron 10-24. I only want to take 2 lenses on my trip, but not sure which 2. With the wide angle only reaching 24, would that be a problem not having the 25-49mm? Also how different are the 18-55 and 10-24? I'm leaving on Aug 28th, so need help!

I have an 18-55 and a 10-20 for my Canon. The difference is very significant.
When I'm shooting landscapes I travel with the 10-20 and a 28-105. For general purpose travel I have the 10-20, a 40mm pancake lens and a 55-250. The 40mm plugs the gap nicely and it is tiny - does Nikon have a similar lens?

You will get distortion with a 10mm lens. Bring the 10-24 and accept the fact that life ain't perfect.

You are going to want a superwide angle lens (10mm or so) for those wide open vistas, and a telephoto lens for closeups of wild animals.

Consider taking 3 lenses; a superwide, your normal 18-55, and your 55-300. That should cover everything.