Hi K,
The problem is what you can do without affecting your credits.
Under the table things:
Dog walking? You could walk people's dogs (elderly, full time workers). My friend CFF used to provide dog day care and sometimes "boarded" a dog. She charged £8 to 10 a day to watch your dog - two walks, lots of attention, medication administered, etc. Overnight she charged £12 to 15. But the dog was with her family in her house -- not in a concrete cage. She only kept one dog at a time -- but she made about £250 or more per month.
I think taking in ironing or doing housecleaning requires the least investment and people are always willing to pay or those services.
Three mothers from my daughter's primary school set up their own gardening service. I hired them one time to do a big weed sort out. Two ladies -- three hours -- £60 - every bed (and there are loads) were weed free. (I have asthma and wasn't up to it.)
There is a military wife who will come to your house and valet your car - inside and out. She charges £50.
A lot of people do things like make and sell jewelry, crafts, baked goods, etc. I had a friend who very successfully did mending, made curtains, slipcovers, etc.
I worked with a maths teacher who did painting on weekends and in the summer.
I have a friend who refurbishes furniture.
I have a friend who has been paid to scrapbook people's baby books, wedding albums, anniversary photos, etc.
I have a friend who makes mobiles and sells them.
I knew a military wife who gave private swim lesson, another who taught voice, another who taught violin, racquetball, tennis, etc.
I knew a military wife who was qualified to do medical coding and did it from here in the UK for the doctor she worked for in the US before her husband was transferred. I think she paid U.S. taxes on her income and the doctor paid for her computer equipment and Internet.
I have a friend who qualified as a masseuse, bought a table and did appointments during the day whilst her kids were in school and two nights a week when her mom could sit.
You could do a manicure qualification, then invest in the gel nails UV light and provide a home service. The same goes for learning to do threading, facials, etc.
My new neighbor teaches piano from her house, as does my daughter's tutor.
I've been offered money many times to do hemming, alterations, make costumes, make piñatas, decorate cakes, prepare scrapbooks, provide childcare, tutor (French, German, English, History, etc.), teach skiing, swimming, do word processing, edit, etc. It's amazing what skills you could provide to others.
I'd like to do people's Christmas shopping and gift wrapping.
As a military brat -- I'm a highly skilled mover... I think I could provide packing service to people who are moving themselves.