In the older Spider-man comics (although it pops again every now and then) he is almost always drawn with webbing in his arm pits as part of his costume.
Have these things been given any function in Spidey canon?
The webs were something Ditko liked and continued to do on and off for years. They were drawn so large, for a time they looked like wings and even other artists questioned if they could have another purpose.
When John Romita started drawing Spider-Man after Ditko left he drew the webbing smaller and smaller and eventually left them off, altogether. If you have never had the pleasure of reading Amazing Fantasy #15, first tale of Spider-Man, no fears True Believer, you can read it here.
When the Amazing Spider-Man #1 came out they included a list of things Spider-Man was able to create with his webbing. This included creating a parachute!