If we are truly thirsty and hungry - it is a physical response to dehydration or the body requiring nutrient.
If we eat when we are hungry and drink when we are thirsty - then that is fine.
The issue with thirst and hunger is that for many people, the effective response to those sensations is intense aversion and fear.
If we cannot eat when we are hungry or drink when we are thirsty then we should merely observe those particular sensations, and any co-arising mental states and thoughts, with a degree of equanimity and objectivity - like a detached observer - until we are able to eat and drink.
The other complication is that many people confuse hunger and thirst for craving for a particular food or drink.
If we are craving particular types of food or drink then we should be observing the phenomenological aspects of craving at that time without mentally indulging or 'rolling' in the craving. The phenomenological aspects of craving and aversion are kaya (body process), vedana (sensation), citta (mental state) and dhamma (mental content/thought).
I am not suggesting that one should not eat or drink or eat or drink particualr things, but to take the time to observe what is going on when we are hungry and thirsty and when we are craving particular things.
“No lists of things to be done. The day providential to itself. The hour. There is no later. This is later. All things of grace and beauty such that one holds them to one's heart have a common provenance in pain. Their birth in grief and ashes.”
- Cormac McCarthy, The Road
Learn this from the waters:
in mountain clefts and chasms,
loud gush the streamlets,
but great rivers flow silently.
- Sutta Nipata 3.725Compassionate Hands Foundation
(Buddhist aid in Myanmar) • Buddhist Global Relief