Where can I find a set of combination briefcase locks?
You can get something like that here but they ain't pretty and have to be riveted on with special tools. Also There's also this place that has real briefcase locks, but it's in the UK and they suggest your local "luggage repair" can do the job for yo...
I used to travel in plane every three months,?
Yes, you can carry on one bag and 1 personal item, such as a briefcase, laptop bag, and purse/ladies hand bag.
What size does carry on luggage have to be?
Has to fit under seat. on most''. You can call your airline and find out what the rules are. It is usually on yout ticket information too. But here is a Guildline--Have a good trip! Airline No. of Bags Allowed Maximum Allowable Dimensions Max Weight ...