Must have been a wallaby or less likely a baby kangaroo. I would put my money on a wallaby. Kangaroo's in Australia are about as tall as humans maybe a foot shorter, so you would need a big shopping bag. Most aussie's if they want a Kangaroo use a Rifle or shot gun if the don't want to skin it. If your ever in Australia and driving in the bush be careful because if a Roo jumps out in front of you, your car will be a write off and you will be lucky to walk away.