In various houses there are sometimes loot containers (sacks, barrels, boxes) up in the eaves / rafters that clearly glow as lootable. But there is no ladder or climbable objects to get up there. Can't jump or climb to get to them.
Good example is Keira Metz's hut.

Is there some trick to reaching them? (Without using the Console mod free-flight mode.)

Sometimes, like in Keira's hut, they're not meant to be looted, they're just containers used as props.

But they still show as yellow lootable containers in witcher sense mode. They could have just used dead items.

Use a stool?

That yellow highlight might be a leftover not intended to be in the game. Minor annoyance, something overlooked in a game of this proportion.

There may be no suitable duplicate dead objects. The point is that they are merely decoration, not placed for the convenience of looting, nothing more.

Such containers usually hold mighty treasure such as vials and broken oars. But if you must have it just keep jumping and sooner or later you will glitch your way through and succeed. Happy hunting!

I also find that irksome.
I wish we could just look up at it and target it that way.

LOL - too true!! But everyone knows, you have loot every last thing in the game, or it's just not complete! =D

The roof is easy to get up on from the rear of Kiera's hut, so I tried slow walking back & forth across her roof while fast clicking the " e ". I got 2 of the 4 glowing objects. One was phosphorus & the other was something green that I didn't see because it went too fast I wasn't really expecting this to work.

____________________________________________________________________________________________
I didn't think about trying it from the roof, but that's pretty clever. Nevertheless, I managed to get the far right one in the corner as you come in the door - it contained a goat hide. This is the only one I managed to fumble around and/or had the patience to get.

I think the bigger info or tip to take away from this is... the "highlighted / glowing" items and containers are not simply props, looks, or ambiance. While CD Projekt Red may have never intended these obscure, seemingly unreachable items to possibly be looted - perhaps as a teasing kind of prank for us OCD or hardcore gamers - though make no mistake... if a player somehow is able, they are absolutely lootable.

I used Aard on the wall below it and when I went outside there were two new loot sacks (phosphorus and white myrtle petals) on the other side of that wall even though the number on the shelf over the door didn’t change or dim. Interesting what’s going on there