1. Inventory has place for portable gasstove:
Combinate the gastank and the gasstove - put it on the ground - look to inventory menue options: you can choose between: "take it" (to inventory) or "take it in hands" - move the crosshair deeper - you see a third option "activate" - press F for activate - nothing will happen
2. Inventory has not enough place for portable gasstove:
Combinate the gastank and the gasstove - put it on the ground - look to inventory menue options: you can choose between: "activate" and "take it in hands" - Press F for activate option - the portable gasstove will working fine