Unlessyour little one is severely delayed they wont need a baby gym - by 8 months they're usually sitting up/crawling/starting to pull themselves up. An activity table with a seat you pop them in, or a jumperoo, would be more age appropriate. You want to avoid using these too much as they aren't great for development but they are a lifesaver if you need to put baby somewhere safe for a few minutes while you go to the loo/make a cup of tea (maybe even drink it if you're lucky!)/put the hoover round etc.
I would highly recommend a carrier. There's some debate about how healthy forward facing front wearing ones are for developing hips, but babies do love the view they give! Your decision. I think one will be invaluable though for helping build a bond between you.
Muslins. You can never have too many!!
A baby change bag with a fold up nappy change mat that lives inside
Some toys, though not too many! Fewer high quality ones are best. Try to avoid flashy plastic talking toys - maybe look at Lovevery or similar subscription services that send you a few high quality age appropriate toys each month.
Books! You'll want a few 'That's not My...' and lift the flap books. 'Where's Spot' is very popular.
Find out if your baby is used to a particular white noise machine or mobile and buy the same one.
A car seat. Look into extended rear facing before you make your purchase.
A nightlight for the bedroom. Black out blinds are very helpful in the summer too!
A kit of 'poorly baby' stuff, Calpol, teething gel and the like.
Bath stuff and washing detergent identical to what the foster carers use. At least at first. It sounds like such a little thing but the baby will feel reassured by familiar scents.
Baby gates and general baby proofing for the house. Your little one will be raiding cupboards before you know it! Look around your living room, baby's room and kitchen and see what potential hazards there are - glass top coffee tables, a TV that can be pulled down, book shelf that could topple etc. and get them sorted. Your garden too.
A snuggledry towel! OK, not essential, but a good idea!