Beltane is a neo-pagan holiday that is typically identified/recognized by non-pagans due to it's accessibility and joyous nature. Named after the Gaelic festival of the same calendar period, modern neo-pagan Beltane observances run the gammut from the historically-inspired (bonfires, May poles) to the (for most) socially deviant (public nudity and sex).
The ancient festival of Beltane is attested to in Ireland, Scotland and the Isle of Man. This day marked the beginning of summer and was tied to many important mythological stories. Beltane also marked the beginning of the pastoral season, when livestock were
sent out to the fields, not to return until the end of autumn. Bonfires were lit and both the people and livestock passed either between the fires or around the fires in an act of ritual purification and protection. In some areas ritual foods, such as grain-cakes, were cooked over the bonfires and shared within the community. Flowers (particularly yellow flowers) were used to adorn houses, people and livestock.
What we now refer to as May poles were more common in pre-Christian Germanic communities. However, their usage was not necessarily tied to observances at the second cross-quarter holidays.
Not all Indo-European cultures have such festivals. In fact, Beltane-esque festivities seem more prominent in cultures with strong pastoral traditions, rather than farming. For example, there is no evidence of a comparable Slavic holiday at the second cross-quarter, although some Slavic neo-pagans now observe a holiday honoring ancestors on or near the same date.