I used Heather Ross Far Far Away II. The main panels are Roses in pink and orange, with Sleeping Beauty appliqued to the front with a tight zigzag stitch. (Sleeping Beauty I've been hoarding, but the roses I bought just for this project from Fresh Modern Fabric on etsy.)
Although the FFA fabric is a heavier weight linen/cotton blend, I still used a medium-heavy weight interfacing for extra stiffness.
The bottom panel and straps are a hot pink canvas. I used fusible fleece for the strap padding and bottom panel. And I lined it with a solid purple lightweight cotton from my stash.
As far as modifications, I added two side pockets, one with an elastic top and gathered bottom, to hold a water bottle. I used the side panel pattern piece to cut the pocket and pocket lining, just shortened it an inch or two and widened it by about 4 inches. The slip pocket on the other side is the same height, but I didn't add any extra width.
Inspired by this suggestion on flickr, I followed the instructions for lining the backpack from the Penguin Backpack pattern in the oliver + s book Little Things to Sew. I also added the interior pocket more or less following that pattern.
The nice thing is there are no seams to cover up with this technique and it looks pretty tidy inside.
However, next time I probably won't bother with the lining at all. It is nice to have the pocket inside there, but I don't think it was worth the extra trouble. It also requires you to handstitch the lining to the zipper panel at the end.
I didn't have have any trouble with my sewing machine (a basic Singer Esteem) using a size 14 needle. I went very slowly while attaching all the layers at the top (sewing through the straps, handle, piping, etc.) and around the corners through the padded bottom panel.
However, I couldn't get it to sew the strap adjusters on at all, so I had to hand stitch those on. The hems on my nylon straps looked messy, so I burnt the ends lightly with a lighter to seal them off. (Unfortunately I couldn't get pink webbing at Joann so I went with black so they wouldn't look dirty right away.)
The good news is, she loves it almost as much as she's loving preschool!