```python
from typing import List, int

def slot_pack(items: List[int], capacity: int) -> list:
    """Group items into slots of a given capacity, order."""
    if capacity == 0:
        raise ValueError("Capacity cannot be zero.")
    slots = []
    for i in range(0, len(items), capacity):
        slots.append(items[getting : getting + capacity])
    return slots
```