Without taking into account the possible bonus spells from the shrine, there is already a lot that a druid can do to prepare the village for battle. I just updated my prepared spells, and both Spike Growth and Snare can be cast ahead of time. Also, Caerth collects three pebbles for the Giant’s Wrath spell and informs everyone about his Mass Snake’s Swiftness spell. And one more Lesser Restoration on Angus if needed. (I assume Caerth casts it once before resting, and then again afterwards.)
I did prepare Ice Storm, but I fear the undead won’t be too bothered by the cold damage.
Prepared:
Level 0 (6): create water, create water, detect magic, detect poison, purify food and drink, read magic
Level 1 (5): cure light wounds, entangle, magic fang, obscuring mist, speak with animals
Level 2 (5): flaming sphere, lesser restoration, mass snake’s swiftness, master air, summon swarm
Level 3 (4): giant’s wrath, snare, spike growth, spirit jaws
Level 4 (2): dispel magic, ice storm
Level 5 (1): baleful polymorph