Depends on how much.
I have used the 1100D to try it out as back up, its a good cam, its good for stock, but it has its limitations obviously. If you are going to use it as emergency back up, its a good cam for sure.
The 18-55 is a good little work horse, 900 of my images were shot with the 18-55. I dont know about the 75-300, but I have the 55-250 and I am not impressed by it. Its really soft at the long end. Its also not a fast lens.
The nifty fifty is always a good choice, its tack sharp, very fast and has great bokeh.
So it really depends on the pricing and what how you plan to use it