A normal day of eating reduces the days without food to 0.A creature who drinks less than half as much water than they need in a day must succeed on a DC 15 CON save or suffer 1 level of exhaustion.A suitably large creature can be treated as terrain for the purpose of jumping onto its back or clinging to a limb.Once you make any ability checks necessary to get into position and to get onto the bigger creature, the smaller creature uses its action to make an Athletics or Acrobatics check contested by the targets Acrobatics check.Food can be stretched out by eating half as much per day, which counts as half a day without food.
If the creature succeeds, it moves to a space next to you.
A PC drinking more than half the amount of water they require during the day but less than the full amount must succeed on a Constitution saving throw or advance one level of exhaustion, or two levels if they are already suffering from exhaustion.
Constitution represents a largely passive set of 'skills' which have more to do with enduring than performing a specific action the PC can become proficient in.
When out of breath, a PC can survive for a number of rounds equal to their Constitution modifier before they drop to 0 hit points and begin to die.
A PC must eat one pound of food per day in order to subsist.
If you make an attack while hidden, regardless of whether it hits or misses, you are no longer hidden.