To achieve this you must use 6 different gadgets in each of the 5 missions.
This is definetly a little easier if you buy armour with atleast 6 inventory slots. (this can be done with out the armour however you will need to rely on finding enough gadgets in the level)
With you new armour buy 6 different gadgets, i recommend the sound generator, emp charge x2, health, epinepherine x2, mine x2, any grenade x2. Depending on the armour you may not be able to carry 2 of each item but if you can then do so.
At the start of any mision use 1 of each gadget straight away (if you have 2 then you have a spare to use in the mission). The only one that you have to wait to use in the health but use that when needed and the sound generator can be used numerous times.
During the 5th mission that you do this, after you use the health the achieve should pop up.
There are not set missions this has to be done on so the choice of missions is completly up to you.
As mentioned in the comments by Vannos - the cheevo should pop when you use the 6th gadget during your 5th mission of having used 6 gadgets and you need not wait till the mission ends.