if you did 3 alternative days of full body heavy strength training, what would you do on other days?

I do about 3 to 4 days of heavy lifting.... depends on the week and the kids, on the days that I do not lift I will do circuit training which can sometimes be moderate to extensive depending on how my coach is feeling that day. Or I will get on the treadmill do a jog/ run. It just depends on how I am feeling after a good leg day all I want to do is an easy walk

I do 3 days of heavy strength training (2 body parts per day) with about 20-30 minutes of cardio and a couple abdominal exercises each day, do about an hour of cardio on 1 day (usually intervals on the treadmill) and a 30 minute abdominal workout, and yoga on 1 day. Then I take 2 days off, usually the weekends.

I might do lighter (cardio) circuits that include movements I don't get on my lifting days.

I am all over the place. I usually do 4 days of strength. The other days depend on how I am feeling. If I am sore, but want to do something, I swim or walk. I will get at least one really good cardio day, hopefully two that is usually HIIT or intervals of some sort.

Once you lift heavy enough (300lbs+ barbell squat) you shouldn't really do much on the rest days save for... rest. Maybe some yoga / light movement and walking. Save your strength for the days you lift!

Monday - 15 mile easy flats ride AM/Lift PM
Tuesday - Hill repeats on the bike.
Wednesday - 15 mile easy flats ride AM/Lift PM
Thursday - 12 mile Tempo/Time Trial ride
Friday - Rest Day (walk/yoga/etc)
Saturday - easy 5 mile spin to the gym to lift and 5 mile cool down spin home
Sunday - 30 mile ride.

Note that my lifting is periodized to train in various rep ranges...I don't lift "heavy" all of the time. I tend to do cycles of undulating periodization where I have a heavy day, a moderate weight/moderate rep day, and a light weight high rep day; cycles of 3x 8-10, and cycles of low weight high rep stuff. My long heavy cycle tends to be in the winter when I'm on my bike a lot less...I do some short cycles here and there, but really, too much heavy work in the weight room interferes with my cycling.

Rest. Since the weights were progressively getting heavier, I needed to focus on recovery. I was able to tolerate more stress, so I added some extra sets / accessory work after all the main lifts.