For all you can hold in your cold dead hand
Is what you have given away.

Joaquin Miller (1837-1913) American poet [pen name of Cincinnatus Heine (or Hiner) Miller]

“Peter Cooper (Died 1883),” ll. 11-12, In Classic Shades and Other Poems (1890)
    (Source)

This phrasing of the sentiment seems to have been made by Miller, but the sentiment itself predates him in various ways. See, for example, Martial, Epigram 5.42 (AD 90): "You keep thus always what you gave."

Edward Gibbon, in his Decline and Fall of the Roman Empire,, ch. 61 (1776), notes the epitaph of 15th Century Earl Edward Courtenay of Devonshire:

What we gave, we have;
What we spent, we had;
What we left, we lost.

Miller was himself quoted by Edwin M. Poteat, President of Furman University, in his poem "What You Have Given Away" (1909). Poteat put the phrase in quotation marks, but is sometimes still given full credit.

Elbert Hubbard may have been borrowing from Miller in his Little Journeys to the Homes of the Great, Vol. 12 "Great Scientists," "Haeckel" (collected in 1916, but published earlier), where he writes:

We keep things by giving them to others. The dead carry in their clenched hands only that which they have given away; and the living carry only the love in their hearts which they have bestowed on others.

Finally, often in the variant form "All we can hold in our cold dead hands is what we have given away," the phrase is today often identified as a Sanskrit proverb. The universality of thought means it may well have an ancient Indian inspiration, but the language may indicate a tie to Miller's poem, as promulgated. The "Sanscrit proverb" appears as such in Hoyt's New Cyclopedia of Practical Quotations (1922), but not in the 1896 edition. This may be taken from a letter to the editor, New York Times (1908-07-25) by Emily Noble, identifying this as the translation of a Sanskrit proverb.