muji cotton
lot and lot of muji cotton

What's he's using now? MOV Double Barrel is the best root beer ejuice to date, IMO. US juice, so might be harder to find but it has that ye olde root beer taste to is. Not that fake F&N shit.

What nekkidgramma means is: generally speaking there's 2 kinds of root beer. One is the traditional kind of root beer and the other is a very sweet and vanilla-ey kind of cream soda/ice cream float-ish flavor (eg A&W's sasparilla). You'll have to determine which type he likes first.

muji cotton can be baught at many vape shop
rather than purchasing a flavour that he might like or dislike
i would suggest you buy accessories
like coilling set ( but does your dad DIY his coil?? ) 

Muji cotton and yes, it's a must have for vapers. Muji outlet nationwide. Make sure to grab only the unbleached ones, not the pearly white ones. So what's kinda of hardware is he's using? The tank, mod, yada yada. Well I think he's okay with the juices then, andyng38 said it best. There are 2 kind of root beer, sassafras and wintergreen. The old A&W uses sassafras and I think MOV too uses them in their juice. Taste aside, I'd think the best thing you could give him is a nice bottle of juices. For a gift why not splurge a lil bit and grab some US juices? Word of the wise, a small bottle could cost you RM 100 depending on said ejuices.