I know the issue about dual logging. If you're playing with four characters it will be a hell hard to to make them participate evenly. Not even to mention that this is a real bummer... I don't think everyone's able to do the same than you, tru, and for the one who can do it, well all good for them I'd say (after all it's quite the hard work to get such a result, we're only human after all).
Ip address checking is not an option unfortunately. Talking about mac address : one can use several laptops (even if it's not handy) or even better, using virtual machines on the same computer. Talking about ip address : what if some people share the same address than you ? Family, classmate, etc. They would not be able to play as well.
Of course, checking mac address would be a good start and limit a lot players abuses on the rare drops.
Anyway, I was wrong with my ideas (contribution, RNG for all, etc.). I just posted a lot of bullshit in the end and I am sorry for that.
People should just use either :
1) Janken (Midori) : People get along and play rock/paper/scissor to know who get the drop, japanese style
2) Rules of ultima (Colorado) : call your hunt, make people agree on it and if someone ninja report...
3) Wild play and Respect : First to pick up get it, or can decide to give it. The second time this drop appear, it goes to someone else.
4) Helping each other (Fyrewolf) : once someone get something they return the favor (might works very well especially between friends/team mate, otherwise it's pretty utopiste)
Or a combinaison of some of the above. Why not...
Don't be afraid to play with others and to share ! Be a little bold !
There's no danger. Try it.