Great advice above. By April the chance of seeing snakes will be low between Canberra and Melbourne. I tend to walk with a stick and bang it on the ground. The vibrations scare them away. The stick is also useful to poke into holes to make sure it isn't home for an animal. Gloves are sensible, as is the compression bandage for a snake bite. Regarding the red backs, they have distinctive fluffy white eggs the size of a pea. If you see eggs the parents won't be far away. You can buy ice packs that are dry until you activate them which is the way to treat red back bites. Kangaroos are plentiful in Canberra, they are dumb and usually hop away if you approach and wombats are nocturnal. Wearing long pants in the bush areas is recommended and covering ankles with socks or gators also helps with ticks. I know it sounds like everything wants to eat you, it's quite fine, you may find more pretend plastic animal containers (snakes/spiders/lizards/birds) for caches than the real thing. Keep that stick handy. Also, if your heading to Adelaide you should check out what kind of BIG geocaching events might be happening in South Australia at that time. Have a great trip.