Among Friends

[stevieb]

Many tote bags with minimal structure, even inexpensive ones, come with a piece of covered cardboard for that very reason. 

[NYCLatinaMe]

I usually purchase an insert or a "handbag base shaper", which are readily available in Amazon.  There are many sizes available, so you may find a nice finished one.  When measuring to purchase, I deduct about 1/4"-1/2" from each side, depending on what the inside of the bag looks like, like fat seams, lining.  There are vendors that will cut a custom base shaper for you, but I haven't tried that because one never knows what the bag will look like with the shaper until it's inserted.  I have bought material and cut my own.  It's a hard piece of plastic that some vendors ship rolled.  Need a sharp blade to cut it.  When it comes rolled, it needs to be straightened.  I left under a pile of books for a few months to accomplish that.  They work well, but i prefer the nice pre-made ones, or an organizer insert.