Was this used to actually hold whiskey? I would be concerned of smells that could stress your gecko out. As tools that i would use is difficult to say. There are many tools out there that would be better than others, but tools that the average person have in their home wouldnt be the best. Since it is wood and metal bands, a saws-all with a blade meant for wood filled with screws would work, but not saying it would turn out perfect or not get ruined. You could always sand it down after cutting. I use saws-alls a lot, and the cuts are never perfect. Are the bands removable? if they are, a band saw would cut with better precision and have a better cut, but unless you know someone in construction or wood work, i doubt you have one in your garage. And you would then need to cut the bands to size, which could be done nicely with some tin snips if the metal bans arent too thick. It would be more likely that you or someone you know have a table saw, which i think would do a good job if you can remove the bands and have someone that knows what they are doing cut it, because you will have to get your hand very close to the saw to make the cut.
I work construction over the summers, so I can only think of tools used on a construction sight. So if it were me I would try to remove the metal bands and make the cut on a table saw, band saw, or saws-all. A table saw would probably be the easiest and cleanest, and band saw wouldnt be bad but would require a steady hand because it doesnt have anything to hold the barrel steady and at the right distance to make the cut. A saws-all would be messy and not a smooth cut, you cut sand it out smooth but would require more work and the possibility of ruining the barrel.
If the metal bans are too thick to cut with tin snips, a wheel grinder would cut right through them. Or a plasma cutter, but i highly doubt you have one of those haha. The possibilities of tools are endless. It is all narrowed down to what you have access too.