¹ Certain features allow you to make more than one attack, grapple, or shove with this action.
² These actions are optional and can be found on pages 271-272 of the DMG.
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.
A suitably large creature can be treated as terrain for the purpose of jumping onto its back or clinging to a limb.
If you are hidden, or when someone can't see you, you have advantage on attack rolls against them, and they have disadvantage on attack rolls against you.
You can grab a creature which is no more than one size category higher than you.
Using at least one free hand, you make an Athletics check contested by the target's Athletics or Acrobatics check. You can also grapple an enemy to climb on top of it.
Therefore, Constitution checks are more uncommon than other ability checks and are usually made without adding a proficiency bonus, although situational bonuses may still apply.
NOTE: An ability check is different from a saving throw; players can be proficient at Constitution saving throws.