One thing I've started doing since about Feb 2011 is using a pedometer to keep track of how far I walk throughout the day. It's been wonderful for me because at the end of the day, I can mentally align it with how I feel and after a week or so I picked out patterns in how I feel. So now I've got a pretty good sense of what I can manage throughout the course of a day without over-botching it (.6 miles over the whole day is my limit) and I know when to stop (if it's a situation I have some control over). It's also nice because I know what to expect at the end of the day after I come home from work; I can guess how I will feel and can rest extra to prevent crashing or just to reset my energy. Plus I get a general sense of how much walking certain activities take (it's surprising how much I walk around my apartment getting ready to go to work, making dinner, etc) and can plan my day around ones that fit well into my allotted steps/distance for the day. I highly recommend it to anyone! My pedometer has been quite the little lifesaver. I've gotten quite a bit of use out of the Omron HJ-112 Digital Pocket Pedometer , and it's quite reliable.
And then! I got this AMAZING gift for my birthday in November from my beaux. It's a bit more expensive but he knows someone who works for the company so he got a hefty discount. My new best friend-- Fitbit Wireless Activity/Sleep Tracker, Black/Blue ! It's a pedometer/accelerometer that can transmit your information wirelessly to your account on their website. This way you can track your activity throughout the day on a graph (I love graphs! such a nerd I am). You can also wear it on a wristband at night and it tracks the quality of your sleep. And it can count steps (like up a staircase). Not that I can take stairs haha, but maybe one day it might be a useful feature ;) Anyway, you can see your history and it plots a little graph of your sleep and your distance and such over the past 30 days. I'm sure this is way more useful for people who can make actual progress over the period of a month, but sadly there's only noticeable progress over periods of a year for me, c'est la vie.
Anyway, I'm attached at the hip to my pedometer, quite literally. If I leave home without it for even a few hours, I feel almost lost because I haven't tracked that bit of steps and have an incomplete understanding of how much I have left in me. I don't know how I did it before! Is that sad? Maybe a little :) But it's so useful!