New York (CNN/Money) - Why let something like taxes get in the way of a good time?

As last-minute filers flood into post offices nationwide, they're finding a diverse collection of groups marking Tax Day in grand style.

Picketers will be protesting taxation. Marketers will be giving away free samples. And of course, there will be millions of actual taxpayers, who are expected to race to 38,000 post offices nationwide to mail their returns by midnight.

Snapple is just one company using tax day to promote its brand.

The rush "won't tax the nation's mail system," says U.S. Postal Service Spokesman Mark Saunders, who apparently can't resist a good pun -- nor the opportunity to point out that despite its efforts on April 15, the postal service is not directly supported by tax dollars.

Many offices will be open right up to the midnight deadline. (To find post offices in your area that are open late call 800-ASK-USPS or go online at www.usps.com, to find a location nearest to you and their hours of operation.)

Events at post offices aren't sponsored by the mail service. But since the sidewalks and other areas around the buildings are public property, anyone can show up.

And they do. In droves.

"April 15 has come to have a carnival atmosphere," agrees David Mazer, manager of public affairs for the Southern California Postal Service.

This year, for example, taxpayers who go to the Los Angeles-area Airport Post Office on Airport Boulevard will get a free video tape of the 20th Century Fox movie, "Drum Line."

In Orem, Utah, Krispy Kreme will be giving out free doughnuts from 6pm on. In Des Moines, there will be free ice cream from Blue Bunny. And in Salt Lake City -- free massages from noon to 3, courtesy of the Myotherapy College of Utah.

New York City's main post office on 8th Avenue between 33rd and 34th streets -- which expects some 20,000 filers Tuesday afternoon alone -- has won a national reputation as the most boisterous place to be come April 15. This year promises to be just as busy.

Snapple, the beverage company, is sending two larger-than-life gorillas and a giant banana to give away free samples of its new drink, "Go Bananas," and bananas for any last-minute filers who skipped lunch to get their return in.

Not into fruit? No problem.

Get your Terra Chips...

Butlers dressed in tuxedos and white gloves will pass around bags of Mediterranean and Zesty Tomato Terra Chips from silver trays for a "five-star tax day event" at the New York post office.

Meanwhile, Popeyes Chicken & Biscuits, the national chain, is showing up at post offices in New York, Atlanta and New Orleans to give away coupons for its newest "Po' Boy."

The sandwich won't be available nationwide until April 28. But the chain thought tax day -- when people may be feeling poorer than ever -- would be a good time to give out free samples, said company spokesman Kevin Crum.

All that could be just the tip of the iceberg. Pat McGovern, spokesperson for that post office, said she had been fielding calls for weeks from people who wanted to show up.

"One person called from Los Angeles. They're bringing some sort of tent and lights. They asked me, 'Can you save me a parking spot?' '' said McGovern. "I told them, 'This is New York City! Please!' "

Don't be surprised if your post office attracts a protestor or two. The Libertarian Party, for example, usually makes appearances, and tomorrow is no exception. In fact, the party will show up twice at the Main post office at North Capital Street and Massachusetts Avenue in Washington, D.C.

Its daytime protest theme will be "taxation without representation." Protestors return later in the evening for a "tax slavery" protest.

Meanwhile, some festivities will have a certain regional flavor.

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Take Nashville, Tennessee. This year, the Grand Ole Opry kicks off its Tuesday night concert series on April 15. Meanwhile, local post offices in the Nashville area expect to process 1 million returns on Tuesday. To celebrate the confluence of these two major events, postal employees will collect tax returns at the Opry from 5 p.m. to 10 p.m.

The Standard Company will be giving away free samples of its "Goo Goo" candy bars at the Opry tax drop-off. The candy bar -- a cluster of peanut, caramel, marshmallow and milk chocolate -- is well known in the area. Some have speculated the name of the candy bar is an acronym for the Grand Ole Opry. Others say the candy bar sounds like a baby because it's so good, babies know to ask for it.

Anyone who needs last-minute tax help will be pleased to learn that tax advisers from H&R Block will also show up at the Opry to dispense their wisdom, such as how to file for an automatic three-month extension. (Not close to Nashville? Not to worry. If you want last-minute help, see our story, Last chance battle plan.)

Meanwhile, Nashville Post Office spokesperson Beth Barnett has advice to offer last-minute filers: "Use the correct amount of postage," she said. "The IRS won't accept returns that have been returned" and re-sent after April 15.