I had a similar gap - DD was 21mo when DS was born (now 3y9m and 2yo). My top tip to myself that I have developed over time is to only plan one thing a day. I used to try to cram in a whole load of stuff, and then everyone got overwhelmed and tired and things would go wrong.
I always make a rough plan including meal plans in the morning. I check the weather, work out what essential things I need to do - e.g. food shopping, drs appt etc., then plan for one outing e.g. park, farm, zoo, cafe, playgroup.
Having bag ready to go is a great idea - I still haven't got this down properly; am forever being caught out without a change of clothes! And it's nice to have lunch ready, although sometimes I think the day goes quicker when you actually have things to do like preparing lunch, sorting stuff out, baking etc. that you can get DC involved in.
It does depend a lot on what your DD is like - my 2yo DS is now playing happily with his vehicles by himself, and will do this for a good long time, whereas at the same age (and even now) my DD will spend no longer than 5mins willingly playing by herself.
We used to do a lot of playgrounds (I found I could manage breastfeeding and pushing swing at the same time if necessary!, otherwise just kept DS in pram as long as I could); playgroups are brilliant for letting older one go off and play whilst you sit with baby, or someone holds baby for you whilst you have a cup of tea.
Also have lots of books around so you can try and look through a book with DD whilst feeding baby.
Sorry, that's totally incoherent, but if I try and go back and edit it into sense I'll probably get fed up and just delete it. Good luck for Friday; it'll probably be much easier than you are anticipating.