Healthy Eating, some obstacles...

I am a 24 year old female, I'm 5' 6" and weigh 140lbs. I recently moved in with my fiance and he doesn't exactly have the most healthy diet (fried food, a lot of meat/ very few vegetables, prepared foods, chips, soda, etc.) and, while he is extremely fit not a pound overweight, I've found myself putting on a few pounds in the past six months. Mon-Fri my fiance and I rarely eat together due to conflicting work schedules, but it's hard cooking for just me. My main issue is when I buy produce on grocery day (usually Sunday) I have a hard time using it all before it starts going bad. Veggies that will be cooked, like green beans, I usually buy frozen, but I like fresh fruits and vegetables as well, especially baby spinach and various types of lettuce for salads/to put in wraps (I find that the bagged baby spinach begins to wilt by midweek). If I lived next to a grocery store I'd just go everyday and buy what I needed fresh, but I live in a very small rural town and the nearest grocery is 15 miles away. Does anyone have any tips on keeping produce fresh longer? And how do I cook for one without ending up with a bunch of leftovers that will never get eaten? Any help would be wonderful, I'm really trying hard to stick to a healthier diet.