volunteering roles that don't require regular commitment?

[HopingtoHelpSomeone]

Does such a thing exist?

I want to meet new people and have enjoyed volunteering before.

Unlike before I can't commit to a day each week as I need to see an elderly parent (staying with them as they are 300 miles away) for a few days now and then.

Everything I can see online needs a commitment to a person/ shop/ school, etc on certain days of the week.

Ideally I'd like to be part of a 'bank' and called on when needed.

Outdoor/ Heritage? Wildlife trust / National trust, /countryside volunteers. It's not all heavy labour tasks - species surveys, guides.

I can't think what it is called, but there is a charity (are charities ?) that support young care Leavers as they start their adult lives.
It is about mentoring and again can be quite flexible in terms of when you meet - sort of replacing the role that a parent would do for an 18 - 25 year old. You aren't there for a "every Tuesday evening" type commitment, but an 'as and when it suits' type arrangement.

However, if you want to get to know the same group of people, then I think your best bet is something like the fundraising group for the Hospice.