Ooh, you lucky thing, sounds fab! It depends on your budget, but yes to apple dunking and all the lovely games others have suggested.
Also, have tables set up with different activities and instruction sheets (Pinterest is your friend here!) - pumpkin carving; make a Halloween puppet - www.pinterest.co.uk/pin/67272588153582667/?lp=true or www.schoolingamonkey.com/shadow-puppet-templates/
If you're after decorations have a look at your local charity shop as well - ours has a great display at the minute with a huge soft toy spider in a red waistcoat in the centre, then bits of cotton wool stretched around him to make webs, and fancy dress costumes and dolls and things around him.
Other activity ideas - keep the balloon in the air for as long as you can (I'm always amazed how people love that one); Hallowe'en themed charades or paper quiz with a small prize at the end for, say, the first back, the most accurate, the one with the best picture of a skeleton etc; guess how many sweets in the jar - closest guess wins the jar; some of our family used to have a game where you have a big black bag of clothes, hats, sunglasses etc, you all stand in a circle and someone plays a song as the bag is passed around, if you're holding the bag when the music stops you have to take an item out and wear it. Game stops when the bag is empty, winner is the one with the fewest or most clothes at the end.
Also, if these Youtube lists are any good go ahead and use them:
www.youtube.com/playlist?list=PLBHb7QCHL6zPIwozmSArn2sMm1fbV7HGd - Halloweeny songs
www.youtube.com/playlist?list=PLBHb7QCHL6zMxfh60o2eq6g9YqPwPQPZo - I called it Retro dance party, it's more just daft dancey songs than anything else
Have a great time though.