When Samuel leaves the pub for the night of the stag he has a leather headdress with a stag skull and antlers on his head. When they have a break of the hill he has a cap with antlers on his head.
In the opening scene, young girls are dancing around a maypole. They have clearly been dancing for a while, as the ribbons are wrapped around the top of the pole. Seconds later, in a close up, there are no ribbons wrapped around the pole.
Throughout the episode, Beltane is given as 4 May. It is actually 1 May (although fertility rites such as The Stag were often performed the night of 30 April, sometimes known as Walpurgisnacht). In addition, while some Beltane fertility rites were, indeed, incorporated into the modern Easter, that festival is more generally descended from Eostre, the festival of the Spring Equinox.
Stag night is so called because stags are male which denotes a male only Affair prior to marriage and does not have its origins in Beltane as suggested by Mrs Barnaby.