Countryside Marchers are holding a Liberty Night party in Weston Street.
As many as 3,000 guests are expected to attend the eve of demo party at the Bridge. Attractions will include banner-making, a fashion show, music, fire-eaters and entertainment.
Organiser Lucy Stoddard says: "It will be the place to be seen. There's no better place to meet the heir to a title and half the county."
Admission will cost £20, to include food and drink, with profits going to the Countryside Alliance.
Meanwhile pro-hunting Americans will be joining Dorset huntsmen for a party on board HMS President opposite the Oxo Tower. The ship is handily moored on the line of the next day's march.