The tradition of cooking pancakes the day before Ash Wednesday emerged because people were using up the rich flour, eggs, sugar and milk that they couldn't eat during the fasting period of Lent. In modern times very few people fast throughout the 40 days and nights but why not see how frugal you can be with food over the next month and a bit? You could try a leftovers dinner tonight, or make tons of pancakes and use them for part of dinner on the next day. Or see how cheaply/sparingly you can cook your meals for. Lots of foodie alternatives for Lent have turned up in recent years; not cooking, going veggie, going vegan, eating on a dollar a day and I'm sure you can find and think of more, so why not pick one and try it?
Alternatively you could pick something to give up that would green your life. I briefly considered giving up the car but it just isn't practical at the moment, too much volunteering going to remote no public transport areas. I will use Lent to have a new boost of cycling enthusiasm though, especially as it's getting lighter and lighter in the mornings now.
You could even turn the whole idea on its head and start a new habit for 40 days. Only use things that can be recycled or reused, buy one organic or Fairtrade item a day, turn the thermostat down a degree every week. Maybe take up a hobby that doesn't use electricity, like crochet or reading. There are so many possibilities it's a bit daunting just thinking about them all.
Whatever you decide to do, or not do, during Lent good luck. It's the little changes we each make (and the bigger ones the government does) that will help to turn the whole world green. Keeping something up for 40 days is hard enough but we just need the motivation and passion to keep us on the right track. The beautiful nature and environment around us, and the desire to protect it, might just be enough.