This Month of the Holy Souls in Purgatory is a good time to remind ourselves of some spiritual practices of the past that have been neglected in recent decades.
As belief in the doctrine of Purgatory has waned, fewer people pray for the Holy Souls. And far fewer people engage in the practice of "offering it up"--offering up our daily sufferings, toil, and stress for the good of the souls in Purgatory.
Pope Benedict XVI referred to this practice in his weekly Angelus address on Sunday, November 4, 2007:
Truthfully, the Church invites us to pray for the dead every day, offering also our sufferings and difficulties that they, once completely purified, might be admitted to enjoy the light and peace of the Lord for all eternity.
When we offer up our daily sufferings, we benefit, too, because we learn better to cope with the challenges of our daily life. Whenever we find ourselves in a bad situation, we should remind ourselves that we're offering it up for the Holy Souls, because the merit of our offering increases when we cope with the situation with Christian charity, humility, and patience.
Children, too, can learn to "offer it up," and they're often eager to do so, especially if they can offer up the trials of childhood for a beloved grandparent or other relative or friend who has died. It's a good way to remind them that, as Christians, we believe in life after death and that, in a very real sense, the souls of the dead are still with us.
(A Memento Mori marks a tomb in the Church of Santa Maria sopra Minerva in Rome. "Memento mori" is Latin for "Remember, you must die." The image reminds us of our own mortality and the judgment to come. Photo © Scott P. Richert)

Yes. “Offer it up” is a common expression with us. It is sort of the Catholic version of “suck it up.” But it means more than simply to “endure and have courage.” It suggests giving your endurance an eternal value.
I was always told to offer it up to for the Holy Souls and have always said this to my children, Thankyou for putting it so clearly that now (although they are all adults)they can understand why, my children are going through that stage of uncertainty about there religion but I know that all the little things they have heard all their lives have stuck with them and that this will eventually bring them back (just like lost sheep)