My nans home did portraits of the residents. Nans hair was done, some lippy and mascara. Strangely though, a company came in with animals and accessories. Nan had a pink feather boa around her neck, a sparkly tiara and a pigeon, yes, a pigeon sitting on her shoulder! Its was the loveliest pic of my nan, but also the weirdest on so many levels!
I too was going to suggest some sort of gardening activity. Bulbs for spring or fast growing crops like raddish, lettuce etc.
Do you have a bird feeder in the garden? Make fat balls for the birds?
Painting- oil, water or acrylic. A life drawing class. Sketching. Paint by number or provide large sheets with a pre-printed outline stencil on there- for those less able to just do it free hand.
I don't know about the legality of bringing home cooked food in, but are the staff from a range of countries? Each bring a plate of something from their home country for residents to try. Multi-national day with flags and different foods. 1 activity could be making the flags the week before for the event. Or if residents are from different nations, they could dress in something from their country, or a select few stand up and talk about something unique about their home country.
Masseuse. Not for a full body thing, but seated and on their neck/shoulders, or hands and feet etc.
Silent disco with lights, glow sicks etc
Show and tell. Each resident presents and object and explains to the other residents why it has meaning/how to use it etc
Is there a garden? Get a few night vision cameras, put out water and cat/hedgehog food and if you capture any animals, have a film night or blow up the pics to show around