We do a lot of combat in the DungeonSports Coliseum. I try to stick to the rules as written as much as possible, but sometimes the PHB and DMG don’t give you all the information you need. Here I site other sources as needed.

Q. Can a creature cast a spell with verbal components while under water?

A. Yes. Any spell can be cast underwater. If the spell has verbal components, things may get a little more complicated. A creature that can breathe underwater can cast the spell normally. A creature that can’t breathe underwater can cast the spell but afterwards, they are no longer holding their breath. This means they begin suffocating (see Basic Rules).

This is confirmed by Jeremy Crawford.

Q. Can an object with a glyph of warding cast on it be moved to a new location with a bag of holding, or created in a bag of holding and then removed to be used?

A. No. Moving an object from one plane of existence to another is moving the object more than the 10 feet specified in the spell. An article on dndbeyond confirms that moving an object in and out of a bag of holding can be ruled as more than 10 feet of movement. I rule it so. The distance between one plane of existence and another is essentially infinite.

Q. Can I drink a potion or administer a potion to another creature as a bonus action?

A. No. Consuming or administering a potion takes an action. 5e Dungeon Master’s Guide p.139