No, but there's wiggle room
The druidic focus and holy symbol are well-defined in the PHB. They are written like exhaustive items in a list. But if you interpret the word "might" as listing items in a partially complete list, you could get away with anything (the DM willing).
Druidic Focus. A druidic focus might be a sprig of mistletoe or holly, a wand or scepter made of yew or another special wood, a staff drawn whole out of a living tree, or a totem object incorporating feathers, fur, bones, and teeth from sacred animals.
Holy Symbol. A holy symbol is a representation of a god or pantheon. It might be an amulet depicting a symbol representing a deity, the same symbol carefully engraved or inlaid as an emblem on a shield, or a tiny box holding a fragment of a sacred relic
Meanwhile, an arcane focus is very open. It can be anything designed to channel the power of arcane spells:
Arcane Focus. An arcane focus is a special item -- an orb, a crystal, a rod, a specially constructed staff, a wand-like length of wood, or some similar item -- designed to channel the power of arcane spells
As for Bards, they need to always use a musical instrument. But the full list of instruments is not listed in the PHB, and so you have a wide latitude of defining what is a "musical instrument". Can you cast via music box? What about a wine glass (you can certainly make music with wine glasses)? What about a coin (since you can make music with a coin)?
I suggest to check with your DM on what they will consider instruments. A typical answer would be anything like drums, lutes, flutes, and the like. A creative flavor could be added like the examples above.
Musical Instrument. Several of the most common types of musical instruments are shown on the table as examples. If you have proficiency with a given musical instrument, you can add your proficiency bonus to any ability checks you make to play music with the instrument.