It sounds like for some folks, bubble wrap and foam would be perfect landscaping materials. 
Good point brought up by other posters: if your weather doesn’t allow you to enjoy the backyard much (snow in winter, bugs in summer), then don’t invest too much in building out a firepit area. A patio is a must for backyard grilling, but the rest of the area can be spruced up with plants and beauty bark before sale. Plant a willow where the water tends to collect. It will drink up a lot of water. Even a small, weeping one can improve drainage.