It is difficult to give a specific answer to this question as the revenue sources that contribute less to the national budget vary depending on the country and its economic policies.
However, generally speaking, revenue sources that contribute less to the national budget are often those that are either smaller in scale or have lower tax rates. For example, revenue from fines, fees, and licenses may contribute less to the national budget than revenue from income tax, corporate tax, or value-added tax (VAT).
It's worth noting that while some revenue sources may contribute less in terms of total revenue, they may still play a significant role in specific areas. For example, revenue from customs duties may not contribute as much to the overall national budget but may be a significant source of funding for the country's trade-related activities.