Do not buy heavy boots just because the event contains the word walk.
An easy dry route may be perfectly comfortable in supportive footwear you already own. Mud, loose ground, wet rock and longer distances can create a stronger reason for trail footwear or boots.
Buying the wrong specialist footwear before you understand your own fit can be worse than starting with something familiar on a suitable route.
You probably do not need a giant hiking backpack for an ordinary social day.
Water, food, personal essentials and a layer do not require expedition luggage. A comfortable small backpack you already own may be completely adequate.
Large bags create a strange temptation to fill the empty space. Pack from the event requirements outwards instead of from the backpack capacity inwards.
Technical extras should solve a problem you have actually encountered.
Walking poles, gaiters, specialist base layers and expensive shells can all be useful in the right circumstances. They are not a uniform starter pack for joining other adults on a walk.
After a few real days, you will know whether your feet get cold, your jacket traps heat, your bag annoys your shoulders or you regularly walk steep terrain. That evidence is more valuable than a generic best-gear list.