We've never had that many toys around the house. As a pediatric occupational therapist, I am schooled in the ways of using what you got. As for my own family, we've found that creating new uses for ordinary objects increases the fun. But kid stuff tends to multiply on its own. I've witnessed it. It's scary.
Of course, when we're traveling, the few things we do have must be narrowed down even more. It's easy to limit the size of what we bring: the boys each have a Trunki suitcase, which holds five gallons of stuff. That sounds like a lot, but it's not when you add in comfort items like blankets and a favorite stuffed animal. However, it's a very concrete visual for them to know that they can only bring what they can fit in their Trunki. So that's the rule. In general, I don't think it's my job to carry their toys. It either fits in the Trunki or it doesn't come.
When we got to the Netherlands, all we had was what came over in these suitcases. It quickly became apparent that we were lacking a few things. But only a few, which is good. Here is what we currently have:
a soccer ball (we mailed this, obviously)
colored pens and journals
2 small board games (one we mailed and one we added when we visited Legoland)
a deck of cards
hotwheels, small trinket items
small shape sorter for the toddler (we added this)
The kids have also made good use of some kitchen items, empty boxes, couch cushions, blankets, and the great outdoors.
Here is what I feel like we are missing:
a few more games - endless entertainment in our family
building blocks (legos)
train set - they often combine the train set with some lego structures
outdoor sporting equipment such as bicycles or a ride on toy for the little one
An option I have used in the past is to keep more toys, but rotate through them every few months. When we had storage in our attic, but not so much in the kids' bedroom, I kept a few toys in the play area, and the overflow went into a container upstairs. Every so often I rotated out a couple toys and replaced them with toys from the attic. It kept the toys fresh and their interest piqued. They always wondered what would show up in their toy boxes. And by the time an old toy made it back downstairs, it was new again.
What am I forgetting? It's easy and sometimes necessary to hold onto toys for the next child or "just in case." But that is a matter of currency - how much is the space those old toys are taking up worth to you? Less than the worth of the toys that are taking up the space? The answer is different for everyone, of course. At our house, we place value on having a calm, chaos-free space for the things we have, and we always somehow manage to find something to play with.