Send a plan, not a vague wish
'We need to do something soon' is a lovely sentiment and a very comfortable place for a plan to retire. Give the invitation a shape: Saturday afternoon, a short walk, then somewhere warm. Let people know when it starts and roughly when it ends.
Try: 'Walk and a hot drink on Saturday? Thinking 3 until 5. Nothing fancy, just want to see you.' Two hours can be enough. You do not have to fill a whole day to make it worth leaving the house.
Choose one anchor, leave the rest loose
Pick the part that matters most: a view, a cafe with comfortable seats, a browse around a familiar neighborhood. Check opening hours, accessibility, weather and the likely cost before sending the plan. Give everyone an easy way to say if the budget or walking distance does not suit them.
You can look at the shops without making shopping the activity. You can bring a flask instead of buying a drink. The point is being somewhere together, not creating evidence that everyone had an expensive afternoon.
Make room for a pause
Think about prayer times and a suitable place to pray before the outing rather than improvising when everyone is already hungry. Ask the group what they need. A little preparation is kinder than assuming everyone's routine is the same.
Keep a simple weather backup too. If the walk is washed out, the warm drink can become the whole plan. A plan that can bend is more likely to happen.
Let one thing become the memory
The photo can be imperfect. The cake can be shared. Someone can leave early. You are spending time with your friends, not directing a campaign for friendship.
Take the picture if you want it, ask before posting anyone else, then put the phone down for a while. The nicest part of the afternoon might be a conversation that would never fit in a caption.