According to the description of the druid's Wild Shape feature:
You choose whether your equipment falls to the ground in your space, merges into your new form, or is worn by it.
Assuming a druid is chained up via non-magical chains. Would the druid be able to make the chains fall to the floor via Wild Shape?
(emphasis added)
You choose whether your Equipment falls to the ground in your space, merges into your new form, or is worn by it.
Items restraining you are not your equipment, just like former allies who are attacking you are not your allies. As such, this rule would not cause the chains to automatically drop.
Note that if you wild shaped into something which was the wrong size for the chains (like an insect), the chains would almost definitely drop to the ground (supported by the 2019 sage advice compendium p. 3, thanks to V2Blast for pointing this out):
Can a bound and gagged druid simply use Wild Shape to get out? It’s hard to capture someone who can turn into a mouse at will. Transforming into a different size can be an effective way of escaping, depending on the nature of the bonds or confinement.
If you tried to Wild Shape into something too large for the chains, what would happen is deliberately unclear. Whether or not a beast similar to your size (like a bear) would remain chained is a gray area, and may depend on how you are restrained (and more accurately, depend on your DM).
Your body transforms, merging (or not) with worn items. It's very reasonable to imagine melding out of restraints.
If you are chained to a wall instead of just tied or manacled, this creates an entirely different situation. In this case, I think your options are limited to escaping the bonds rather than melding with the entire structure.
Imagine if an ally places a hat on your head. Is it their equipment or yours? Merely possessing an item makes it "yours" for these purposes. Otherwise at what point do you consider the magic items you plundered yours and not the original owner's?
Simply enough, is the item completely under the control of the character? In this example, a set of handcuffs would be completely under the control of the character (that he can't take them off is an irrelevant distinction). But if the cuffs are chained to the wall, then they are not entirely under the character's control and they are not equipment.
This same test is useful for determining how other spells, such as Invisibility, act. There are some edge cases that are hard to cover: for example, a fisherman's rod is certainly under his control and qualifies as equipment, but the bobber floating slack on the water are not entirely under his control, and the fish caught on the hook underwater is definitely not under his control. There is no perfect test that will handle every situation, which is why God invented DMs.
For a Druid in handcuffs - the handcuffs change with him, which would allow him to run/swim/fly away, but when he returns to human form he would still be wearing them.
A Druid chained to a wall - the chains would not change with him, as they are not entirely under his control and do not qualify as equipment. If the druid picks an appropriate form, he could slip out of the chains.
