What made me use my bike more was when I got panniers, a rack and a trailer. I can now pickup medium sized items from a store like a bike stand or a large amount of shopping.

The panniers can be used to move a smaller amount of shopping especially when combined with a backpack. You can also just put heavy things in the panniers to make you work harder with more weight on the bike.

The thing is to think what else you can use your bike for than just pleasure free time rides that way you get to ride it while also accomplishing a task, possibly even a task that you would have used the car for anyway.