To expand on a couple things:
For what it sounds like you are looking for, walking outside would probably be the better idea than going to a gym. It's easier, usually less time consuming, and it's much easier to get motivated to do. It's true that once you are in the gym you would have someone telling you what to do, but GETTING to the gym is the tough part. If your not someone who is really in to working out, going to the gym regulary is not easy over time.
Keeping logs of what you are doing is a great idea. Just remember, don't make it too difficult. Simple notes to keep track of what you are doing is all you need. The simpler you make all this stuff, the better.
Just as important is plan your days/weeks out as much as possible. On Sunday while you are watching the games, grab a pad and make a quick list. Monday: Walk Outside after work. Wednesday: Golf Thursday: Treadmill before work. Etc...
If you want to get real serious, plan your meals. (To me it sounds like you want to remain casual and drop a few pounds, so planning the activities is a good place to start).
Once you have your plan....STICK TO IT.
For most people who just want to get a little more active and drop a few pounds over time, walking really is a great way to do that. It gives you exercise and can be relaxing at the same time. Gives you time to think and enjoy your environment. Go with friend and catch up on football, take the wife (if you have one) and catch up on life. It's definately a good idea.
If you want more than that, planning is the key. Pick a work out and diet and plan as much as possible. Plan your meals, workout schedule, and goals, and keep to it as much as possible.