What does so severely had we dealt with our supper the previous night that we previous night that we had little to eat but the biscuits mean?

The phrase "so severely had we dealt with our supper the previous night that we had little to eat but the biscuits" suggests that the meal the speakers had the night before was consumed with great intensity or enthusiasm, leaving them with very little food left for the following day, specifically only biscuits. This reflects a sense of overindulgence or perhaps a lack of foresight in managing their provisions. It conveys a feeling of scarcity and the consequences of their actions from the previous night.