To trigger an object glyph, a creature must "open" the object:

This powerful inscription harms those who enter, pass, or open the warded area or object....

But also, the caster can "set all of the conditions":

You set all of the conditions of the ward. Typically, any creature entering the warded area or opening the warded object without speaking a password (which you set when casting the spell) is subject to the magic it stores.

So if a caster wanted to store a number of different effects in a small container, are their options limited to small, openable objects? Or does the "set all the conditions" clause allow you to glyph pebbles that pop when they hit the ground?

Extra Credit: if the small object must be openable, could you cast glyph of warding on an egg?