These are wooden boards on which some kind of prayer ritual is performed (if you know more about this, then let me know). It involves the devotee kneeing at the end and then rolling their body flat onto the board by extending rollers along the length of the board. All the boards and devotees face in the same direction and the ritual is performed many, many times. I saw mostly women doing it. You'll also see Buddhist monks, pilgrims and exiled Tibetan's walking around on the elevated perimeter path around the temple carrying prayer beads and chanting.
I sat near some monks whilst they were being called to prayer. It's a nice experience to see them chant and perform their Buddhist rituals whilst only sitting a few feet away. They seem to like having you observe them. They come from all of the nearby monasteries and so where different coloured robes to indicate where they originate from. Tibetan monks where red whilst yellow is worn in southern countries.
Bodhgaya and the mahakalla caves are pilgrim places, so a LOT of beggars will gather there. Families send their elderly and children there, because they can´t work otherwise. Now dont give milkpowder to mothers with children, the´ll just sell it back to the shop-owner, and don´t buy sweets for kids, rather organize some proper food, or give them money. They´ll spend it for better stuff than chocolate, because it´s too expensive for them. Some beggars there are so fastidious, that they wont take your 25 peisas (or less)!
If you want to increase your good karma by giving money to beggars, change some papermoney into coins infront of the main stupa. You´ll make a slight loss of course, but you´ll have plenty of coins. They are sold in small plasic bags. If you start throwing paper money at them, you´ll be surounded by dozens of beggars within seconds, and won´t be left alone for the rest of your stay!