"Хлебнуть сполна" means that someone has had so much sorrow, grief or sufferings that is difficult to imagine that someone can have more sorrow, grief or sufferings. In English the closest idiom is "to eat the bread of affliction".

Usually this phrase is used in negative sense. Has nothing in common with "to get drunk". Хлебнуть сполна = натерпеться (to have had enough of smth, to endure enough) Examples: They have gone through a lot of sufferings. She has got her dose of abuse.

The verb “хлебнуть” has the infinite verb “хлебать” - to take / swallow a mouthful (of) – to eat with a spoon something like liquid / to gulp (down) / to spoon up / to spoon out. Хлебнуть сполна – have a drop too much Хлебнуть горя – to eat the bread of affliction Сполна – completely, in full