The Classic Bonfire

"Midsummer Night is the longest day of the year and has been celebrated in some fashion since ancient times.  In Pagan tradition, Litha marked... [when] the days gradually [began to] get shorter as the world descends into the cold dark of winter. Like Beltane, fire is an element of Litha. Bonfires were lit to assist the sun as it journeyed across the sky, changing course and shortening the days."

–Mabon House,
History of Litha⁷

S'mores at the Campfire

Despite what many of us may want to do, it is often impractical or not possible for us to construct a full bonfire to celebrate. A more small-scale, practical alternative is a campfire. Furthermore, the celebration can still be communal and even incorporate some 'non-traditional' elements, such as s'mores, which are forged in the heat of the fire. This is also a good option for those in the broom closet, as it is not necessarily openly pagan. This idea comes from a reddit post⁸ linked below.

Sunbathing

What better way is there to connect with the sun than to lay and bask in it's glorious heat? Sunbathing, or generally spending time outside under the heat of the sun, is a good way to celebrate Litha and show appreciation for the sun at it's zenith. A word of caution: BE CAREFUL! While we may worship the sun, the sun is also to be feared.

"Wear SPF [30+] and apply...15 minutes before going outside. Make sure you cover your body in at least a full ounce of sunscreen. That’s about...a full shot glass. Don’t forget to use SPF on the top of your head if it’s not protected by hair, as well as your hands, feet, and lips...Take breaks in the shade when you get hot. Drink water if you’re spending prolonged periods of time in the sun."

–Healthline,
Is Sunbathing Good for You?⁹