SlipMatch
Two PDFs go in; one PDF comes out with each slip followed by its label, in packing order.
Pair your real slips and labels, see the full packing order including anything it could not pair, and print the first 10 orders.
SlipMatch is free to use today, and there is nothing to buy. It is planned to be part of the $19/month Avyth subscription, which covers every tool with a recurring job — Invoice Splitter, SlipMatch, FBA Gap Auditor and Article 50 Check — not a separate charge for this one tool — it would add: Larger batches than the free tool handles.
It isn't built, so there is no checkout on this site and no way to be charged. When it exists it will appear on the updates page, with the date.
Email support@avyth.com and the person who built SlipMatch reads it. If it fails on your file, say what the file looks like — that is usually enough to fix it.