I have a grey card in my wallet, the same size as a credit card. Easily can be moved from wallet to pants pocket or to breast pocket of shirt for easy access and use in the field when actively needed.

But, it's getting onto years now since I've used the card. I now let the camera operate in auto WB in all situations while shooting in RAW in all situations. I then adjust the K temp and Green-Red tint in LR during editing. You need a calibrated monitor and may need to futz with the values both initially and during a final check of results after editing. I don't click a control point within the image, rather just eye-ball. Use the before / after swap to help eyeball the needed changes.

The auto WB adjustment within LR is usually worse than no change, but the software analysis helps you understand, typically, the direction of the update needed. The auto analysis may make the image too warm or cool, but you can use the direction of the change to determine the update to the original WB / K-temp as determined by the camera. Or, sometimes the LR software will indicate the opposite direction, making an image warmer (higher K temp) when the "correct" update is to pull the K-temp lower from the out-of-camera temp. As you experience and observe the tendencies of the camera and the software, you get a feel for how they work, and over time, can work more efficiently in your editing.

To me, the best aspect of LR is setting the WB on one image and then syncing that change across all similar images. I may tweak the WB further as I work across the images, but usually, after I've "established" the WB for that situation / time of day, I just need to sync across the images and move onto other edits.