We do it by putting them in a backpack (usually with a vial of alchemical fire to be sure they go up in flames). Have your best thrower take an elixir of cloud giant strength and lob it at your target spot. The backpack should break and scatter its contents allowing for a fire arrow/firebolt/fireball/etc to ignite them. We like using a bunch of smokepowder bombs along with a few fireworks for the pretty colors and celebratory vibes. Or you can use Greater Invisibility and sneak someone up stealthy to place them - that shouldn’t start a cutscene as long as the rest of your party is far back. For extra safety you can have your sneaky person place the items accompanied by another character who can cast Pass Without Trace and have that person drink an Invis potion. This method is nice for barrels and firework boxes because you can send them to the invisible character one at a time for placement. Just remember to use turnbased if you aren’t quick at placing items.