If it is less than a fifteen minute walk to where you are going then walk instead of drive. You will get there faster than driving will get you there too.
Getting a bicycle is the next step. A friend who commutese by bike now started just by using her bike to go shopping for groceries 4 blocks away. (get a bike that isa bit upright to ride with a good basket.

Get in the habit of using a small packsack when you walk.
It is surprising how fast your ability to carry stuff increases and it is good for most of the body, not just the legs.