The completion bonus is a small amount of resources given when completing a resource-gathering building:

These bonuses can provide a small boost to a nation's early economy and, with some planning, even be used to 'convert' resources. For example, if you have an abundance of timber but are in desperate need for food (e.g. to research some vital technology), use the timber to create some farms and receive an instant +20 food per farm completed.

The Germans receive an additional 50% completion bonus, e.g. 30 Food Food per Farm built.

When a Caravan establishes a trading route, it receives a one-time bonus of Wealth Wealth, at both cities at the end of route, depending on the number of the Commerce levels researched. Generally, the higher the Commerce level, the more Wealth Wealth obtained.