Lien has a special peaceful place for transitioning your loved one.
Take all of your pet's favorite treats with you, especially the forbidden ones. If not able to eat it, the smell should make them happy.
For people hearing their loved ones voice is a calming thing but for pets maybe touch is more comforting. Whatever sense they have now, feed it as much as you are able.
I (next time) will ask the vet for a little pet Valium to give before we set off to the clinic.
I don't think pets know that they have retirement accrued. To leave their job of making us happy and loved? I wrote a letter to my dear Millie the day before. It helped me some later... and I buried her with it, then planted a beautiful rose bush... so that her love will continue to grow and give to those around her.
It has been 15 years and I still miss her every day!