It depends on what costumes and decorations you would like to create. You can find some ideas for costumes here: http://costumeideazone.com/. As for decorations, the following site has a lot of great ideas: http://tlc.howstuffworks.com/family/halloween-decorations.htm.
Halloween Express and Party City will have a variety of costumes available. Party City will also have paper products, decorations, etc. that you may also need. You may want to get ideas from coworkers as well.
There are plenty of places in order for one to get inspiration to create funny Halloween costumes. However, one might want to check out the best Halloween Costumes in the past to create somethings news via the website the design inspiration.
You can find personalized Christmas decorations at several websites. Squiddo.com has a variety of Halloween themed Christmas decorations for you "dark tree". Or, you can try searching for ideas to create your own homemade decorations.
You can actually learn how to make very simple, very fashionable Halloween decorations on your own. There are some great sites with recommendations on how to create them like Michaels and Youtube.
Spirit Halloween and Anytime Costumes each carry a wide variety of cat costumes on their websites.. Dance shops often carry various costumes including cat ones. Stores such as Walmart and Target also carry costumes for Halloween.
Patterns for children's ghost costumes are available online and from Halloween stores. A person can order these patterns and create their own ghost costumes for their children.
Halloween decorations are so much fun and so easy to create. You can buy some old wine bottles and decorate them with candles and black ribbon. Or burn new titles on old hard covered books that say things like "Book of Spells."
You can use your everyday clothing to create unique costumes. Here are some examples of costumes: Cowboy, secretary, politician, teacher, student, ghost, zombie, and so many more.
You could use white lights for both, though better choices would be orange and black for Halloween - white would be okay. You could create a Scarecrow for Halloween, then dress him as Santa for Christmas. That would be creative.
Around Halloween, virtually every store that carries costumes shares unique ideas to create the perfect look. Many websites provide photos and ideas for those that are unsure of what to dress up as. One reputable store is Party City and they come out with a catalogue of costumes each year.
Using jackolantern stencils over orange and black construction paper can be a good way to decorate for Halloween at home. They can also be used over tissue paper to add a more eery appearance.
There are websites devoted to helping you create ideas for costumes such as www.costumeideazone.com and www.101halloweenideas.com. You could also try asking friends for ideas.