To be very full of things, with almost no space between them.
Siksik can make people think of being crowded or having a lot of things in a small space.
Examples:
The box is siksik with toys.
The room is siksik with people.
The siksik bus was very full.
The jar is siksik with marbles!
The closet is siksik with clothes.
The car was siksik with clowns and balloons.