If your wedding venue is out in the sticks or perhaps just a little bit hidden, setting up a few signs to let your guests know they are in the right place will avoid a lot of confusion (and phone calls).
And if things are a little bit spread around in your venue, make sure you have a few directional signs to let guests know what's happening where. Or even where the toilets are! Some venues are a bit of a rabbit warren, or in the case of festival style weddings - very spread out! So giving guests an idea of where they should be going will be so helpful.
It's unlikely you've forgotten to sort out a seating plan (we hope) but when it comes to displaying it, some couples haven't thought it through. If it's a mirror or a printed plan, ask your venue if they have an easel or another way of displaying it. If it's hung, have you ordered everything you need to be able to hang it?
Always, always, always a last minute one - the confetti. Many couples don't think much of it, thinking that it's so common they will be able to order it on Amazon or pick it up from Tesco on the way to the wedding....
But in many cases, venues need bio-degradable or even dried petals because of their rules (some historical venues will only allow white petals only because of fear the colours will damage floors!). Make sure you know what you are allowed, and leave plenty of time to order it from a provider or from your florist. They will need to make sure they have at least a few weeks to sort it out, as they will also need to order enough flowers to provide it.