Thought I'd add my two penneth, as I'm kind of in the same boat!
I'm preparing for my first LDW (Ridgeway) and to get myself to a decent level of fitness, I've done the following:
Healthy balanced meals, no snacking except on fresh fruit, but Friday night is treat night!
I walk home from work once a week (13-15 miles depending on my route) and go on a hike every sunday of about 15 miles. A waterproof OS custom map of your local area comes in very handy here. When I do those two walks, I tend to fill my backpack as much as I can with unnecessary weight, so I get used to carrying it and it helps strengthen my muscles, in preparation for all the weight I'll be carrying on the Ridgeway.
In the last 4 months I've lost close to 3 stone, and have developed leg muscles that could probably deflect bullets, so it seems to be working pretty well! Also, on the days when I walk the 13-15 miles home from work, I don't need to feel too guilty about having an oggy's pastie for lunch
Changing little routines can help too - when you do your weekly shop, leave the car at home and walk to the supermarket if possible and load all your shopping up in a suitably sized rucksack.
I hope some of that is useful!
