Leaving any pet for 36 hours - hamster, dog, cat, tortoise, rat, mouse, flamin' mongoose...is wrong. In my opinion.
Why though?
I wouldn't leave a dog alone for two days but that's because they are more high maintenance than a cat or an animal like a fish/hamster/tortoise that will be quite fine on "minimal maintenance" of just being fed/watered and not exercised/played with for a day or two.
Obviously anything longer would require more care but an overnight trip is fine for most small animals provided you plan appropriately.
I have two indoor cats, I leave them alone all the time and they've not murdered each other yet.
I would have no problems leaving the two of them for 36 hours - they always have dry food down in a large bowl and it normally lasts them 2/3 days when full. They get wet food every other day. They have a large "watercooler" type bowl, when full it can last a week (though I change the water every three days as both cats actually prefer "stale" water.
If I was going away from Friday morning to Saturday evening I'd make sure the dry food bowl was full, feed them their wet food, fill the water bowl (and leave the bathroom tap to drip with the plug in - over the course of 2 days it won't be enough to fill the sink and even if it did it would easily be dealt with by the overflow hole - so there's fresh water if they did manage to knock over their water bowl (for the first time ever) and make sure they had fresh litter trays.
They'd be fine for that amount of time, at worst they'd sulk for a while when I got home, but they get over that in a day or two.
Any longer and I pay my younger cousin to drop in every day to feed them, refill the water and clean their litter trays and leave the TV on for a few hours