Sweden has municipal, provincial, and national elections all at once. Here's how they work:

You takes your municipal-party ballot(*) and stuffs it in one envelope(+), your provincial-party ballot and stuffs it in another envelope, and your national-party ballot and stuffs it in yet a third envelope. You seals your envelopes, comes out from the hush-hush sooper-*sikrit* election booth and steps over to the table where the volunteer functionaries sit, behind the ballot urns(&), and show some ID so they can cross you off in the ledger (Yes, even if the ID checker is your old "junior high school" history teacher, he *will* insist on seeing ID -- just to give you a lesson in how things are supposed to be done, I think), and then you stuff each ballot into the correct urn.

How can you get this right, you ask, when the ballots are inside sealed envelopes -- how would you know which sealed envelope goes in which urn? Well, you see, the ballots are colour-coded, and the envelopes are special election envelopes: They have two lower corners cut off(%), so the corresponding corners of whatever paper is in them are visible! The pre-printed text is much more towards the center of the paper, so that can't be seen. (I suppose if you did a write-in, and doodled all the way out there, then you only have yourself to blame for the functionaries noticing that "that crackpot probably wrote 'Donald Duck' again".)

You just stuff the envelope with the protruding white corners in the urn with the white top, the one with the pale-blue corners in the urn with the blue top, and the one with the pale-yellow corners in the urn with the yellow top.

OK, sure, if you're electing deputy sherriffs and dogcatchers, you'll need more colours -- but the principle should work all the same, AFAICS.

(Another alternative would of course be, "so DON'T vote for every frigging functionary under the sun on the same day.")

HTH!

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(*): Usually pre-printed by the parties wot want you to vote for them, but blank papers are available for you to write "Donald Duck!" on, if that's how you feel.

(+): To preserve the secrecy of your vote -- wouldn't want the volunteers who oversee the process to sneak a peek at your ballot.

(&): Big wooden boxes, actually. (Well, probably plywood, to be *quite* precise.)

(%): The envelopes also have a glued-in piece of string along the top, under the flap you glued sealed, IIRC. This is presumably to make them easier to open, by just pulling on the string, so the election functionaries don't have to use more lethal forms of letter openers.