I don't have any rule books to read and the last rule book I had was dnd 2e, but this question came up at lunch today at work. Is it possible to place live objects in a bag of holding. For instance, say I wanted to smuggle my dwarf friend into a building. Could I place him in the bag of holding, carry him into the building and then retrieve him? What about a creature. Maybe I would like to take a rabbit into a building that has a no rabbit policy. I can't just chain him up to the rail outside. So could he be placed in a bag of holding?
Yes, you can do this.
As long as the creature is 200# or less and less than 20 cubic feet in volume.
I believe it is currently undefined as to the air requirements of a living creature so if you're going to keep them in the bag for a longer length of time, you'll need a ruling from your DM.
I don't think there are official rules on this, so I think you're going to have to ask your DM.
If I were the DM, I'd say
A Bag of Holding only holds 20 cubic feet. That's not a 20x20x20 cube. That's a 2.71 foot cube. A rabbit would fit, but your dwarf friend might have difficulty squeezing into a space that small.
For reference, a standard coffin is 84"x28"x23" or 31.3 cubic feet. Could you fit into two thirds of a coffin?
Another thing to consider is that this is a bag, not a sack, so the size of the opening could be a factor - another thing for your DM to decide.
There's also the issue of how long you could survive inside the bag. Mythbusters did an experiment on being buried alive. Jamie, during the dry run, was able to remain calm and composed and lasted about 50 minutes before starting to run out of air.
Using that as a baseline, we can figure out how long a creature would survive in the bag based on it's mass. I don't want to get too mathy here (hit me up in chat if you're interested), but assuming a dwarf is about as dense as a human and has an average weight of 190 lb, the dwarf could last about 29.3 minutes before exhausting the oxygen supply in the bag. Per Starving, Thirst and Suffocation add another 3 minutes or so for a grand total of ~32.3 minutes before your dwarf buddy suffocates (unless of course he's got a Ioun Stone of Sustenance).
The rabbit would obviously last longer, but I don't know the average mass, density, and oxygen consumption rate of a rabbit to do the calculations.
Absolutely. You should check the capacity of the bag though. A Deep-Pocket cloak holds 100 cubic feet or 1000 pounds of stuff, but each compartment of the cloak is limited to 10 pounds. So it holds most rabbits, but no full grown dwarf would fit in there. I'm not sure if bags of holding have similar restrictions.
Also, if they're going to be in the bag a while, you'll probably want 4e's equivalent of this: http://www.dandwiki.com/wiki/SRD:Bottle_of_Air
Since there's a ritual (Self holding bag) for folding the bag into itself and putting it into an extradimensional space pocket, I doubt much anything so mundane as holding living beings is off limits. As Pat said, the only limit is what fits in weight or volume.
You can, and most answers assume that once inside your living being would begin to use up air until they suffocated.
I believe this only happens if you close the bag. If you leave the bag partially open, your being would be able to stay inside indefinitely assuming they have food and drink and don't poison it with their biological waste.
When you open the bag there is no woosh as it fills with air so I assume it's like a stargate to an empty void in that there is a membrane-like barrier that stops water, air, poisonous gas, etc. from rushing in or out just by opening the bag. The dimension in the bag has no air and the occupant can only hold their breath for so long. You can't just hold it open, you'd need to figure a way to pump air in. Or maybe have the occupant press their face to the opening from the inside. carrying around a face on your rogue's belt would still make a stealth mission a lot easier than asking a fully armored knight to sneak past anyone.