Prayers for the dead are very much a part of Catholic life. (Catechism of the Catholic Church, 1032, 1056, 1371, for starters)
I think that, in addition to praying for the repose of the souls of people you know personally, praying for these celebrities would be a good idea. No pressure: just a suggestion.
Given American cultural assumptions, I'd better point out that I do not intend to imply that the three people whose position put them in America's spotlight are particularly in need of redemption. We all need help.
For example, the United States Conference of Catholic Bishops has "FOR THE REPOSE OF THE SOUL of POPE JOHN PAUL II / A Novena of Prayer" on its website, as a .pdf document.
Don't Know What to Say? No ProblemPrayers made up on spot are just fine. I see them as having a conversation with God.
On the other hand, the Catholic Church has prayers for many different occasions: ready to go. Starting from the idea of spiritual warfare, you could see knit-your-own prayers as the equivalent of the old musket-loaders, where you had to prepare each shot by hand, in the field. Memorized prayers are more like cartridges in a clip: ready to fire when the need demands.
Anyway, here's a traditional Catholic prayer for the dead:
Eternal rest grant unto them oh Lord, and let perpetual light shine upon them.
May their souls and the souls of the faithful departed, through the mercy of God rest in peace. Amen.