My personal favorite option, maybe it's because I take my laptop (his name is Ringo) with me everywhere, is the laptop bag. They're commercially available in cute prints and styles and if you don't have a laptop, you can use them for folders and notebooks. This one on the right is my favorite one I own. It's got a cute Alice in Wonderland pattern and the White Rabbit charm is removable! I got it at ShopKawaii.com, which also sells Sanrio and San-X merchandise and bunches of other cute things perfect for a lolita life. They do online shipping all over the world, and everything is just so cute! If you're looking for something a little less sweet, I really like some of the options from Modcloth. Their items are a little country and a little classic, like this deer print bag. If you're feeling crafty, you could make or get a plain colored one and decorate it to your liking!
I know I've talked about these before on here somewhere, mostly because I adore them. Sometimes you see Japanese students with these briefcase-like bags for their books, both in Anime and in real life. The lolita fashion movement co-opted this bag style and made it fit into the lolita aesthetic. They are sort of like the above laptop bags, but usually they are styled more after briefcases. Both brands and off-brands (like Taobao shops) make bags in this style. However, as you probably can imagine, the Japanese brands charge far more for one. The price ranges from $100 - $250 for a bag like this, it's a little much for a purse. However, some Taobao shops make their own versions. They're far cheaper, at around $40 US. However, they are also often smaller, and "not meant for heavy items." So it just depends on what you're looking for and what you're planning to use the bag for.
This is what I really needed for school. If you have a sweet style or you wear things inspired by decora and fairy kei, then it's extremely easy to find backpacks. Sanrio sells a whole bunch of them that range in size and style. However, for other styles, it's a little more tricky. For gothic and punk styles, there are bags like the coffin one on the right that have backpack straps attached. The only problem is that they aren't always the right size or shape for school books or a laptop. In the way of backpacks for classic, there isn't really much. You're much better off getting a school bag to match. And all the sub styles. I have this theory that every sub-style in lolita can be made by combining two or more of these main styles. For example, country is just sweet combined with classic. But more on that later. As long as it works with your outfit and is functional, go for it! 9/10 times, no one is going to notice that your backpack doesn't quite match your clothes.
Do you have a bag that you like to use the most? I have this black purse with a bow as the snap closure that I use pretty much everywhere. It's big on the inside and blends into my black-based coordinates well. It's also cheap and durable! Thanks for reading~