In all seriousness, patience to wait for them to get closer if you are unable, for whatever reason, to get yourself closer to them. As long and as fast a lens plus a good tele converter as you can afford and are able to carry/use. In parks a zoom is handy because you never know at what distance the animals will appear at and it won't leave you fumbling around changing lenses. A camera or lens that features image stabilization is helpful too. At home for birds you could put out food sources to get them closer and shoot from an improvised blind. If your end use for your images is placing them on the net, viewing on a big screen TV or 8x10 prints then there are a few small sensored "bridge cameras" that should do nicely with zoom to about the equivalent of 600 mm or so. Photographing wild animals can be, by turns, very frustrating one minute and very easy the next.
Bob