An afternoon bag does not need to contain a second nursery. Start with the length of the outing, how your baby is fed and where you can change them. A walk near home, a visit to a relative and several hours of errands create different needs, even if the same bag carries them.
Put the changing supplies together: diapers, wipes, a suitable changing mat and a way to keep used clothing separate. Choose the number of diapers from your baby's recent pattern and add a modest spare allowance. There is no single correct count for every baby and every afternoon.
Pack a complete clothing change in the current size, including the small items you would otherwise forget. A replacement outfit is less useful if it contains a top but no clean bottoms. Check the spare clothes periodically; items left untouched in a bag can be outgrown before they are ever worn.
Make feeding supplies specific
Bring what your baby actually uses and follow the relevant preparation and storage instructions for their food or milk. An insulated pocket is not a guarantee that food stays at a safe temperature indefinitely. If the outing requires temperature-controlled storage, plan that properly rather than assuming the bag solves it.
Keep adult essentials in one accessible pocket: keys, phone and a payment method. A small snack and water for the caregiver can make a long afternoon easier. Do not let those items bury the baby's supplies, especially anything you need quickly during a change.
A familiar age-appropriate book or toy may be enough for a short wait. Avoid filling every spare pocket with entertainment. The bag should still be comfortable to carry and easy to close when used clothing has been added.
Reset when you get home
Remove used items and anything that needs appropriate refrigeration or disposal promptly. Replace diapers and clothes before the next outing, while you can still remember what was used. Leave a brief note if another caregiver needs to restock something you do not have.
After several trips, notice what repeatedly helps and what never leaves the bag. Adjust the contents to your household rather than preserving a list from before the baby arrived. A useful afternoon bag makes the next change or feed easier without making every outing feel like a move.