What's wrong with one of these? http/www.sailwider-smartpower.com/product/multi_socket_plug_adapter_b_s.jpg
Can buy them at any superstore/wilko type shop. If you really only want one plug, you could even wire all of them together in one plug, although I wouldn't advise it, if the fuse started blowing, you'd have a mare finding what's wrong
I use similar older ones on most of my tanks as I live in an oldish house and am short on sockets in most rooms.
As long as your careful and take the usual precautions (making sure the wires are firmly fixed in and that water can't drip/leak onto them) you should be fine.
Do bear in mind that I am NOT a qualified electrician or anything like that! This is just from personal experience of using a similar cable tidy for 15+ years
I use a Power centre on my 2ft Fry tank. Lights and Air pump are connected to it.
Wouldn't connect heater or filter to it though as you would not want to turn them off by mistake.