Maintenance service for low mileage?

[roi]

I only do city driving to/from work, not much chance to get on highway. I have a 2007 Toyota Corolla CE (bought new). Don't know anything about cars ...

1. I have 22,000kms on it now - only had oil changes annually and air filter change (dealership says don't need anything else)
2. fuel consumption is heavy although I'm a light driver (no fast accelleration or hard stops) - ie. I fill up every week and get about 350 kms from a full tank (I do carry quite a lot of items in the trunk, it being Canada and winter, e.g. salt, blankets, spade, extra window washer, etc)
3. brakes are squeaking when applied on slight incline

Keep on feeling something can be done to help my fuel consumption through a maintenance service, but don't know what. Also does brake or transmission fluid get old and need replacing? Brakes are spongy sometimes but rectify themselves, and ride is not as smooth as when new (had tires balanced and rotated).

Thanks for any advice!

[Slaander]

I did pretty much same thing, but I also change the cabin filter every 16,000 km.