Many of the test casess can be written on travel bag. Among 
them most important are :
1. In should be cost effective.
2. It should be durable.
3. It should have enough size to fulfill the requirent of 
trvelling.
4. It should have wheels so that easy to move.
5. It should be secuired (Should have theft protecting 
features.)

etc...

1)size should be as per our requirement.
2)it should easy to handle in rush(able to take in hand &
also able to set on back.
3)color of bag should be proper as per company logo or
attractive,
4)it should have different compartment for
laptop,files,small things like dairy,pens & other.
5)it should be tough against heavy weight.
6)it should be water proof to protect material.
7)it should have proper lock.
8)it should have wheels(if possible).
9)it should have some compartment with zip which can able to
use even bag is locked for regular use things like
calculator,pen dairy.
10)it should not have any sharp edges which can damage any
person.
 
etc...

First of all we need to collect user requirements so that 
we can continue our testing against those 
requirements.After verifying product for user requirements 
we can check for other features which are mentioned above 
by Avinash/sourav.