This is not an exhaustive list. But the hope is that people can do something positive with their political engagement to feel less powerless about the problems we face. Engaging politically is very important too of course, but if you are looking for somewhere to donate your time or money, to make a difference it's a starting point:
Poverty
The Poverty Alliance seeks to influence policies at all level that have an impact on poverty and can create the conditions for a more socially just Scotland
Trussell Trust Organises food banks across the UK
Housing
Shelter Scotland giving advice, information and advocacy to people in housing need, and by campaigning for lasting political change to end the housing crisis for good.
Children and Young People
Barnardos Operates throughout the UK and helps young people with an array of challenges, including mental health, domestic violence, leaving care and poverty]]
Children 1st Scottish Children's charity tackling a wide range of issues, from children at risk, families separating, befriending etc.
Yorkhill Childrens' Charity supports parents and children at Yorkhill Children's Hospital in Glasgow
Women
Scottish Women's Aid Scottish Women's Aid works towards the prevention of domestic abuse. Campaigns and lobbies for effective responses to domestic abuse. Works with local shelters.
Women's Fund Scotland gives money to local projects to encourage or support women and girls.
Older People
Glasgow Old People's Welfare Association - Provides Daycare, Supported Accommodation, Clubs, Advice and more to Elderly people in Glasgow
Disability
Glasgow Disability Alliance Group which aims to be a collective, representative voice of disabled people, promoting equality, rights and social justice.
Adult Care and Support
Turning Point Scotland Provides support to adults with varied complex needs such as learning difficulties, mental health problems, addictions, homelessness, rehabilitation etc.
General Volunteering
Volunteer Scotland
Improving Politics
Electoral Reform Society campaigning to make UK politics better.
I am sure the are lots more local projects and national ones I haven't mentioned. Often these were ones that came to mind or came up when I did a quick search. I know I haven't even touched on the environment or health charities but I don't have any more time at the moment.
I hope they are of use to someone.