Your 18-55 and 55-250mm lenses will cover most of your outdoor, landscape and wildlife shooting needs well. I'd leave the 75-300 at home, its image quality is not as good as the 55-250 and it lacks image stabilization.
Three years ago, I took a T2i, 18-55 and 55-250 along our trip to Yellowstone, Glacier and other sites in the northern Rockies and was very happy with the pictures. I found the 55-250 was long enough to get some great shots of bears, elk and moose.
Also take the 50 1.8 if you think you will be taking any indoor, low-light shots. Your zooms will not be good for that type of shooting without flash.
While you should be very happy with the lenses you have, if you are considering any additional lens purchases, consider an EF-S 15-85mm or EF-S 17-55mm. Both have "L" lens image quality and will be a nice step up from your 18-55 kit lens. Of the two, get the 15-85 if most of your shooting is outdoors in good light and consider the more expensive 17-55 if you do a lot of low-light photography.