High energy rescue dogs & the 3-3-3 rule – what to do with them before the dog is settled enough for training?

Basically the title, lol. I adopted a high energy herding mix this morning and even though we did lots of research and thought we were ready, now that the dog is here and staring at me, I suddenly feel a lot LESS ready. I read all about the 3-3-3 rule and know he needs time to decompress and settle in before we can start training stuff and playing games etc, but I'm only just now realizing I don't know what we do in the meantime.

How do I keep him entertained and meet his exercise/stimulation needs when he's still decompressing?? He would like to be interacting with me or my husband all the time so far & does not really seem to get the concept of toys.