My tomato plants are under attack!

[Pock]

There are very few insects that bother tomato plants, but there are several diseases. The brown/yellowing leaves are a sign of disease. It could be any one (or more) of several. Repotting it into a larger container, as @kevwr1962 recommends is a GREAT idea. Any stress to the plant (such as being root-bound) makes it more susceptible to diseases.
The good news is, the tomatoes themselves shouldn’t be affected.
Have you had your first BLT yet?

No, but I picked one off the plant this morning and handed it to my daughter. She is a big fan of tomatoes. What is a good way to know when to water?

[AV8R]

my potted tomatoes need water daily. The leaves begin to droop if they don't get it.

[Oscar Leroy]

I would also add some nutrients. I'm sure Kelly's has a line of organic fertilizers.

[Pock]

my potted tomatoes need water daily. The leaves begin to droop if they don't get it.

I've been watering daily so when the leaves started to yellow I thought I had over-watered them.