Unfortunately, there are no rulings on the interiors of extra-planar items
The most popular are the Bag of Holding and Heward's Handy Haversack.
The biggest hurdle is that it is never mentioned whether or not items in the luggage can interact with each other. In other words, if I put in a handful of dirt as one action, and a pitcher of water in as another, will I pull out mud?
This is important as if the characters can put items in one at a time, and they cannot interact, then there is nothing to "bump against" to cause damage. Although external forces against the bag may cause a problem to be addressed later.
The closest we can get to figuring out interaction is with the Haversack:
Retrieving an item from the haversack requires you to use an action. When you reach into the haversack for a specific item, the item is always magically on top.
Since the item retrieved appears "on top", there must be something below it. Therefore items do at least interact during the process of retrieval. As a DM, I would go so far as to say that they are always intermingled, but the retrieval process floats an item to the top.
We also can see in the description that it's always described as a "space". The term space does not imply any sort of organization. When you put money in, there is not a special compartment just for holding coins. Nor a separate vault for armor, and so forth.
There is also the matter of orientation. Would putting said pitcher of water in the space always remain upright?
We do know a certain amount of air exists due to the rules of breathing creatures listed for the Bag of Holding. So the items put in do not exist in a vacuum; hot things cool, cold things warm up, and the two may interact and cancel each other out. This also means items placed inside are not in some bubble that conforms to the object.
Now, with all that said, nothing would indicate that exertion on the outside of the bags would have any effect on the inside as items exist in a different plane.
There are rules for if the bags are pierced or torn, but no rules on crushed. So in theory, you could have a T-Rex walk over over bag and it would be fine, so long as one of its claws didn't rip a stitch.
So depending on what the "fragile" item is, the players may or may not be safe.