You can get regular gas carriers (red) from 1.75 gallons to 4 gallon packs - or diesel fuel packs (yellow) get 1, 2, 4 - whatever their vehicle can handle. Kerosene are Blue. Water carriers (white) come in 1 or 2 gallon capacity, and there are various universal mounts and ties that secure them.
They also have road repair, first aid, and 72 hour survival packs in orange. They fit together flat like legos if you want to stack packs side by side.
There are also misc storage packs in gray. They are around $54-60 each, more for the orange packs, and less for the attachment hardware and extras. CLICK HERE to go right to the Rotopax site - there is a plethora of things you can get - and some can stretch out to be added for birthdays, father or mothers days etc… Google around for the best prices. Hurry and order these for a really unique gift and keep your loved one protected!