What do I need with my Canon 600ex-rt?

I invested in two really good flash units (Canon 600ex-rt) with the radio controller for the hot shoe. Can you guys suggest affordable gear to pair with this (umbrella/stand/etc.)? I've committed to taking some senior portraits and I plan to use flash outdoors to help with any harsh light encountered. I'm not a professional and the equipment does not have to be top of the line....but I don't want any junk. All comments and advice are appreciated.

The Westcott Apollo and Rapid Boxes are a nice line to work with my Canon 600 EX-RT's and ST-E3 RT's. Softbox, Strip Light and Beauty Dish Style lighting are available with the two lines above in an affordable option.
Also your standard umbrellas are options as well.
So many modifiers to choose from these days. It really opens up your options.

The first thing i would get is a power pack, like the CP-E4 or similar.
cuts the recycle time from 6ish secs at full power to around 2 - really helps with the flow of a shoot if you aren't waiting ages between shots.

I echo what Echo said.

Yep, this one.

https://www.adorama.co​m/werb2lk.html

For an affordable kit I recommend the following. These will get you started and also last while you continue to acquire other gear and find your own path.

2- Photoflex 45-inch convertible umbrellas
2- Godox S-type brackets
2- Manfrotto or Photoflex light stands
Total cost: $180-250

MPEX used to do a basic strobist kit, stands, brollies and brackets, gels and some other bits and pieces for a really good price.
After years of fulltime heavy use the stands are still working but heavily worn, the brackets are fine, and i have lost both brollies (i know one is in a forest, 3 hrs drive away, next to a big tree stump)

A great portable little kit, and one i used heavily

Thanks!