Wah How to use "In case".

We use in case to express that an action is connected with something that might happen.

• The football referee wears two watches in case one of them stops.                               ( There was a possibility of one of the watches stopping. )
• I will take some food and drinks in case we get lost in the forest.                                     ( I will take some food and drinks before I go to the forest because I want to make sure that I don't get hungry or thirsty when I get lost in the forest. )
• It's a bit cloudy. You should take an umbrella in case it rains.
• You had better take a cellphone in case you need to contact me.
• I think I will wear gloves in case I get cold finger.
• We should leave early in case the traffic is bad.

Note: After in case we never use will even though we talk about the future.
         You should take an umbrella in case it will rains. is incorrect.

The different between in case and if.
    I will take an umbrella in case it rains. (Whether or not it rains, I will take it anyway.)
    I will take an umbrella if it rains. (If it does not rain, you won't take it.)

Wah How to use May / Might as well.

We know how to use may and might in this topic:

Wah How to use "May and Might"

We use May / Might as well + Verb to give suggestions like should, ought to but we usually use this form when you think there is no choice or nothing better to do. 
We often use it when you are not eager about that suggestion.

• There isn't anything to do and I feel a little drowsy. I might as well go to bed now.
• Here comes a bus. We might as well take it. We are already late.
• There is nothing on TV this morning. we might as well watch the comedy.
• You cannot leave before 10.00 A.M., You may as well wait here.
• I am free now, I may as well go shopping with you.
• I have finished all my work. I may as well go home now.
• You might as well tell her the truth. Lying will make everything worse.

Wah How to use "May and Might"

May and Might are the auxiliary verbs as are should,ought to and will. Let's see how to use them.

We use May when we are asking for permission.
    May I come in please? 
    May I borrow your bicycle this afternoon? 
    May I sit here please?
    You mayn't may not leave until you finish your work.
    You may not smoke in here.

We use May when you are not sure or to talk about the possibility of something.
    It may rain today. It mays to rain. is incorrect.
    I may go to the United States next month if it's possible.
    There may be a lot of cars on the road right now.
    I'm so busy today, I may not have time to work out.

Wah How to use "Must/Might/May/Can't be"

When you are sure something is true, you can say "must be". 
        He is speaking Japanese, He must be Japanese. (I am sure he is Japanese.)
        She must be a police officer.(I think she is a police officer.)
        This must be the way to the park. (I am certain this is the way to the park.)

If you are quite sure something may be true, you can say "may/might be".
        He is so late at the meeting, the traffic might be bad.
        John is not at the office now, he may be taking the day off.
        I am not sure but she might be older than me.

And If you want to say something you think it is unlikely, you can say "can't be".
        He is very old, he can't be the student.
        Sarah is at the hospital, she can't be working today.
        This restaurant is very delicious, it can't be going out of business.

Kenny Chesney - Must Be Something I Missed
"There must be something I missed
I wake up in the morning just making a fist
I don't call it living, I just exist
There must be something I missed..."