In case + present tense statement

I am packing some sandwiches in case I feel hungry later
In case I feel hungry = Because I might feel hungry

In case of

This is different. It means "if there is.." or "If something happens..."
In case of is used on formal notices such as fire procedures. "In case of a fire leave by the nearest exit"

In case

I'll come and visit you in case I'm in town is incorrect in English.

In case / If

In British English at least, in case does not mean the same as if (American usage is different). In case refers to precautions, things we do in advance to avoid problems or danger in the future. I have insured my diamond ring in case it is stolen. Take your umbrella in case it rains.

The order of events is:

1. you take the precaution
2. the problem or danger may happen

If refers to the result of a possible event.

If my diamond necklace is stolen I shall get 2,000 pounds from the insurance company. I'll come and visit you if I'm in town.

The order of events is:

1. the event may occur (eg robbery, rain)
2. this will cause a further event (eg money from the insurance company, putting up my umbrella)

In case is, therefore, strongly associated with taking insurance policies. In case of is a phrase often used on public notices:

In case of fire, phone the fire brigade. And is close in meaning to if.

If there is a fire, phone the fire brigade.

In the case of should not be confused with in case of. We use in the case of as a sentence introducer meaning when we look at, or when we consider, usually in contrast to another person or thing we have been talking about.

Hydrogen was found to be a dangerous gas for filling large balloons. In the case of helium, no such problem occurred.