Minecraft wiki entry for Pillager, associated text: 8.5% chance for a crossbow (loaded or unloaded, depending on the crossbow's state when the pillager dies) when killed by a player or tamed wolf; drop chance increases by 1% per level of Looting. The crossbow is of a random durability and has up to a 10% chance of being enchanted at level 5-19, depending on regional difficulty.
5 and an additional 1–3 per naturally-spawned equipment when killed by a player or tamed wolf.
1 ominous banner‌[JE only]/illager banner‌[BE only], if spawned as a captain.
0–2 arrows ‌[BE only]. Each level of Looting increases the maximum number of arrows dropped, up to 5.