Which should I get first?

You are not saying anything regarding why you're contemplating these instruments, whether or not you have played mandolin before, whether or not you have tried these actual instruments, or what sort of guitar/s you have at the moment.

If you already have an electric guitar, then you need to be more specific as to why you may want this one. If it's for an upgrade, then maybe ... just maybe.

The Epiphone brand leaves a lot to be desired in the quality department from my experience; don't appear to hold up very well, although they can play (and look) nice at first glance.

You also need to try the guitar out in person to make sure it's OK. Same goes for the other two instruments of course.

If you don't have an acoustic guitar already, then the DR-100 can be a passable beginner guitar - if you have checked it and it's properly set up.

However, since you play guitar already, I'd go for a guitar that is far superior but not much more expensive. The Yamaha 700 and up series have a solid (non laminate) wood top and are far superior guitars in every respect. There are also many other brands I'd personally pick before an Epiphone acoustic.

The mandolin may again be a passable choice if you haven't played one before and want to try it out. Just be aware that this is very cheap and that low end mandolins tend to be a bit hard to play and enjoy. It is often times possible to have them adjusted so that they play well - other times it a bit of a hit and miss thing.

My advice will be to pick the one that you know you can get the most out of. Just double check everything for quality issues :-)

Epiphone DR-100 Acoustic.

Mandolin DEF!