Welcome to Explorer, a modification for Fallout: New Vegass that aim to expand the original game with a lot of new areas, items, weapons, quests and much more. As the name suggest the mod is focused on exploring discovering new places that are not tied with the main quest.
The Tool Kit is basicly a portable workbench. It works as any other items like Stimpacks, Repair Kit etc... with the difference that this one will bring up the Workbench menu, where you can craft new weapons or build new type of ammo.
This item will be rare to find, but it can be bought on vendors for 60 caps, just be carefull when carrying it as it takes 2 points of weight.
This item may be usefull if you are in a cave for example and you are out of ammo, so you bring out the Tool Kit, craft new ammo and continue the exploring.