Hi Amy, Here are some suggestions to consider...

Supplies for science projects or scientific exploration:
>Small magnifying glasses
>Mini-tape measure and/or ruler
>Pencils and notepads (every scientist needs to record his/her findings!)
>Alka-Seltzer tablets (with a note that they are not candy & are for experiments only; I'd also make mention to parents about that item if included)
>Goggles or funny glasses
>Pocket-size periodic table (example: http://handheld.softpedia.com/get/Educational/Science/Pocket-Periodic-Table-Pocket-PC-15304.shtml )
>Pocket-size liquid measurements chart (http://southernfood.about.com/library/info/blfluidmeasure.htm )

Toys and candy:
>Glow sticks
>Green slime
>Grow-with-water tablets or eggs (typically they have sponge animals inside)
>Gummy eyeballs, fingers, insects
>Test tube bubbles (example: http://www.miamisci.org/store/product_info.php?cPath=67&products_id=767&osCsid=4baf3 )
>Kaleidoscope and/or prism disks (example: http://scientificsonline.com/product.asp_Q_pn_E_3081424 )

I'd also include 'scrolls' of any scientific method tips and/or science experiments you use from Education.com (simply print those pages, roll and then tie with ribbon):
http://www.education.com/science-fair/all-grades/
http://www.education.com/topic/help-child-with-science-fair-projects/

Hope this helps. Thanks for asking!

The Mad Science crew actually supplies the kids with a couple of things. One of them being "slime" In my opinion you don't need to supply more party favors...especially NOT candy!

Make an erupting volcano.  Materials:  foil cake trays or other trays to catch the mess.  Fast Mache, Plaster of Paris, or some other fast acting molding material, vinegar, baking soda, water, food coloring, plastic spoons, small paper cups.  Liquid soap is optional for more interesting eruptions.  Also optional is fast drying model paint to make the volcano look more real.
Place container on tray and mold the volcano around it.  Don't worry if the volcano looks lumpy and bumpy.  While waiting for your volcano to harden you can put left over plaster in a plastic baggie and shape it into something else - dinosauers, animals, people, etc.  Mix a spoonful of water with a spoonful of baking soda and place it in the container.  Then add a drop of food coloring (and liquid soap if desired) followed by a spoonful or two of vinegar.  Watch your volcano erupt.  Stirring it and adding a little more vinegar will make it erupt more.
For snacks, have a bucket of dirt made with chocolate pudding to which is added gummi worms and broken up graham crackers.

Just search pet TickleMe Plant to grow the only house plant that "moves" and closes its leaves like crazy when you Tickle It.
They even have TickleMe Plant Party Favors and Classroom kits.
http:/www.ticklemeplant.com    See video

you can probably have like planets around the room and probably like scientific machines and napkins that say science on it and a happy birthday sign.