Venice might sink from all the luggage guests are bringing to the wedding of Jeff Bezos and Lauren Sanchez … because they’ve got to pack everything under the sun for a bunch of hoity-toity theme parties … so forget about carry-ons!!

Sources tell TMZ … Jeff and Lauren’s wedding itinerary features 3 theme parties, including a pajama-themed bash, so guests will need clothes, outfits and accessories for a wide range of events. No light traveling here.

The wedding will likely have a rehearsal dinner, reception and some cocktail parties … so guests will have a ton of other crap to pack … and we haven’t even gotten to the actual nuptials. At least the weekend foam party required little more than swimwear.

Jeff and Lauren are expecting big-name celebs, titans of industry, well-connected entrepreneurs and more … and all these highfalutin guests will need all of their clothes tailored for the various events.

In other words, preparing to watch Jeff and Lauren walk down the aisle is no walk in the park. Weddings are stressful, even more so when billionaires are involved.

We broke the story … one of the venues locked down is considered the crown jewel of the famous Italian island, Fondazione Giorgio Cini … a cultural center on the island of San Giorgio Maggiore.