Make a Gryffindor scarf by crocheting, knitting or felting. Note that the knit scarf pattern has thick blocks of color instead of the thin lines of the Gryffindor scarf that the older students wear.
Start out with a gold tie (compare prices). Use red fabric paint to add the lines on the tie. If you're using paint and a brush, employ a ruler to help you make straight lines. A fabric pen works much easier in this case and most fabric stores have them in many colors.
Make two thick lines, then skip an inch and make a very thin line. Skip another inch and repeat this pattern.
The Gryffindor Robes
Make your own Gryffindor Robe in any size. I takes just minutes with this easy tutorial:
Hermione's hair is on the wild side as a child, her puffed wavy and sometimes crinkly locks can be recreated right out of the shower. Hang your head upside down while it's still wet. Blow dry your hair while scrunching it with your hand. Rub a dime sized amount of styling mousse on your hands before grabbing clumps and pushing them against your head.
Use a towel to pat clumps of hair against your head to help curl and dry the hair. Once dry, stand up straight and behold your raging afro. Tame it to a nice Hermione volume with some more styling mousse.
Any thin stick can be made into a wand. Peel off any bark and use a piece of sandpaper to smooth down the sides of the stick. For a pointed end, use a small knife to whittle the end of the stick. Shaving the end of the stick should be done with adult supervision. Apply a dark or light wood varnish to your smoothed wand.
The Leaky Cauldron provides a set of instructions for a Time Turner.
I suggest looking in a few local thrift shops for these simple elements. Get a white button-down shirt and a black or gray sweater vest to wear over it. Wear a pleated black skirt, knee-high socks and black dress shoes. Mary Janes work nicely.