Will you ever want to use your bike to maybe pick up groceries or a few things at the store, etc.? If not, just get a large seatpack for your tools, tubes, etc. But if you follow in the footsteps of most newbie commuters, you'll soon want do more on your bike which will require a rack and panniers and/or a trailer. There are some very high end options for this stuff so it can be intimidating but if you look around you can find some cheap option that might get you going until you really know what you need.

Does this help?