If you can get a decent insulator (e.g. cooler), and the other items are significant thermal mass, you should be able to leave them outside the freezer for a few hours without too much trouble. If you want to give yourself a bit more time, you can set the freezer extra cold first, then take the items out. Adding water bottles and/or freezer pads first can also help, especially if the items are irregularly shaped. If you have a fridge, you can also stick them in there, as long as you don't have many items there already, and the ones you do have can stand being frozen; if you fill (emphasis on "fill") a fridge with frozen items, and don't open the fridge, the stuff should stay frozen for hours if not days, even without power.
Once you've gotten everything else out, if you don't care about your water bill, you can speed up the defrosting by pouring hot water and periodically pouring it out (or siphoning it out or otherwise removing it) and replacing it with new hot water. If getting water out is too difficult, you can put most of the water in bags and replace the water in the bags with hot water, and have just enough free flowing water to conduct the heat.
Another answer suggested a hair drier, but air has very little thermal mass, and so does little to defrost items. Simply getting a fan to circulate air will give most of the benefit of a hair drier (cold air sinks, so without circulation, even an open chest freezer will keep items frozen for a while).
For the future, you should wrap your fish in wax paper, and then place it in a plastic bag. You may also want to reconsider freezing 4kg blocks of fish. Smaller pieces will use up more paper and bags, but will be much less unwieldy and easier to defrost.