Maximum Efficiency, Minimum Effort
Anybody who knows anything about judo knows how important gripping is these days. In any contest the judoka with a stronger grip and with more extensive knowledge of grips and grip fighting has the advantage. So, it would be a good idea for any judoka to ensure they have a strong grip.
So, how would you do this? Squeeze stress balls or those little metal things? Well, you might but I certainly would not! Squeezing an object countless times might give you more endurance in the wrist and forearm but the resistance is just too little to build any strength. So, would the best way be to incorporate a load of grip strengthening exercises into your training regime? Only if you have time to add them in during your 45 minute weight session and chances are you don't.
Except in rare cases you don't need that many extra exercises just for your grip. Just adapt your training somewhat. Instead of doing countless sets of wrist curls, reverse bicep curls, etc., just think about how you do your regular exercises. With the weight lifting, use free weights and grip the bar tightly. Pullups work the brachioradialis better than reverse curls as well as a few other muscles. More bang for the buck and a simpler workout. When you do randori, make a conscious effort to do a degree of grip fighting (but not so much that you won't be getting any throws in). Pullups are great for grip strength, particularly if you add weight and wrap your gi around a bar. If you can, wrap a gi around the barbell when doing weight lifting to make it twice as thick and grip that. When doing pushups or squatthrusts or burpees, try to push the ends of your fingers into the floor, as if trying to get a grip on a basketball. Everytime you finish a session and take off your gi, wring it out a few times as if you're trying to get the sweat out. Or you could take a bath towel, fold it over, grip it as tight as you can and try to pull it apart. If you succeed it doesn't cost much to buy another one! Just a few simple methods here and you can actually reduce the time of your workouts.
So, eliminate all those extra forearm/wrist specific exercises and adapt your regular exercises more. If you still want an extra exercise for your grip strength, I recommend rope climbing — one of the best (and most functional) exercises for improving grip strength.
So, ditch the isolational rubbish and thicken the bars, grip tighter, grip fight a bit more in randori, use your gi in the weight room, wring out your gi, "grip" the floor in pushups, and (if possible) incorporate rope climbing into your training regimen
The result? Stronger grip and more time for uchikomi.