Lots of familiar objects can be placed in a row and stacked.
Craft items include stamps, stickers, felt shapes, beads, and buttons.
Boxes are easier to stack and apt to be less frustrating than items like the sponges that spill over.
Toys include blocks, match box cars and Jacob's ladder.
Household objects can include socks, bottles of lotions, cutlery, fruits, vegetables, bars of soap, boxes of tea candles, and soup and rice mixes.
Game items include dominoes and poker chips.
Many people spontaneously start placing objects in a row or stacking them according to customary use. If not, most other people will place the objects where indicated by pointing.