Three sources ranked: (A) items/resource boxes from event bosses -- best; (B) gathering resource tiles; (C) production -- least recommended (monster hunting and gathering beat it). All free/F2P. Boss resource-drop ranking by quantity (x4 RSS types): Azazel 5M, Kraken 4M, Stymphalian Bird 3M, Ymir6 2.9M, Ammit 2.5M, Witch6/Warlord6 2.1M; by stamina efficiency Azazel 400K/stamina, Kraken 320K, Ymir6 290K; Cerberus drops 0 resources. Consuming Return Event (free, repeatable): consuming resources returns more -- spend 2.5B each -> 360M+ each; 10B -> 1.6B+ each; consuming speedups also returns resources. Recommended around Keep 25-31. Do NOT open resource boxes early (food consumed by upkeep, lootable if attacked); avoid Store and Black Market (poor value). Gathering-amount buffs stack: 6 Queen Jindeok (+40%, free at tavern for 21M gold), Korean sub-cities (+3-15% each), Champion's Set (4) (+10%), Monarch Talent Lv26 Gathering Boost (+20%), Mona Lisa art buff (+10%). Gathering speed: maximize general Politics, skill book +45%, Advancement research +180%, King's weapons up to +110%, gathering speedup items +50%, Lv12+ tiles 200K/h, alliance hive buff +25%. Monarch Talent Lv22 Resources Critical gives 10% chance to double a box. Production buffs (passive): Advancement research +170%, Shajar al-Durr +100% (free), production speedups +200%, Shrine offerings +100%/2h, monarch gear +50%, alliance science +15%, hive +35%, Monarch Talent Lv6 +50%. For the bot: gathering is the main free automatable lever; open resource boxes just-in-time, not early.
Original research source: Evony Guide Wiki