The rites of marriage and death are a significant part of most religions. How does Buddhism celebrate these or any other rites?
I think that managing the body after death -- funeral rites -- might be a lay/cultural concern, rather a Buddhist/spiritual one; e.g. from DN 16:
Then Ven. Anuruddha said to Ven. Ānanda, “Go, friend Ānanda. Entering Kusinārā, announce to the Kusinārā Mallans, ‘The Blessed One, Vāsiṭṭhas, has totally unbound. Now is the time for you to do as you see fit.’”
That's often cremation. I think there are rites but that these vary some from country to country.
See also How long to leave a body undisturbed after death? -- i.e. it may be usual or traditional to leave the body undisturbed for at least long enough for death to become apparent.
There is some custom for before death, for example:
The Vinita-vatthu to Pr 4 contains a number of stories in which bhikkhus comfort a dying bhikkhu by asking him to reflect on what he has attained through the practice, which was apparently a common way of encouraging a dying bhikkhu to focus his thoughts on the best object possible. The suttas also contain advice on how to encourage patients facing death.
That may also vary some from one Buddhist tradition to another
See also How to die professionally?
In supramundane Dhamma (Lokuttara Dhamma) marriage (sensual desire) and "rites" are fetters, which stall progress to experience nibbana. Clinging to rites and views is called silabattupadana, which the stream entrant (sotapanna) has shaken off.
Marriage however is endorsed for lay practitioners, given they're at least undertaking the five precepts.
Above said, it is evident that the Buddha rather talked about which qualities husbands and wives should have, and not necessarily how these customs are celebrated.
"In five ways, young householder, should a wife as the West be ministered to by a husband: (i) by being courteous to her, (ii) by not despising her, (iii) by being faithful to her, (iv) by handing over authority to her, (v) by providing her with adornments.
"The wife thus ministered to as the West by her husband shows her compassion to her husband in five ways: (i) she performs her duties well, (ii) she is hospitable to relations and attendants (iii) she is faithful, (iv) she protects what he brings, (v) she is skilled and industrious in discharging her duties.
Parents, on the other hand, have the duty to arrange a marriage, but this has to be understood in the historical context.
"In five ways, young householder, the parents thus ministered to as the East by their children, show their compassion: (i) they restrain them from evil, (ii) they encourage them to do good, (iii) they train them for a profession, (iv) they arrange a suitable marriage, (v) at the proper time they hand over their inheritance to them.
Concerning death, I believe that most Buddhists choose to be cremated (especially monks).
But there is probably no definite answer, since the are a lot of sectarian Buddhisms out there, which are strongly interwoven with i) current society and its customs; ii) " non-canonical customs & teachings not spoken by the Buddha, which have been inherited since forever, to make Buddhism fit into everything; iii) The Dhamma is only concerned about stress (dukkha) & its cessation:
And so, Anuradha — when you can't pin down the Tathagata as a truth or reality even in the present life — is it proper for you to declare, 'Friends, the Tathagata — the supreme man, the superlative man, attainer of the superlative attainment — being described, is described otherwise than with these four positions: The Tathagata exists after death, does not exist after death, both does & does not exist after death, neither exists nor does not exist after death'?" "No, lord." "Very good, Anuradha. Very good. Both formerly & now, it is only stress that I describe, and the cessation of stress."