Step 1: Understanding the selection process
We have three categories of items:
- 6 alike fruits,
- 7 alike vegetables,
- 8 alike biscuits.
We need to determine the number of ways to select at least one item from each category.
Step 2: Finding possible selections from each category
Since the items in each category are identical, selecting any number from each category corresponds to choosing a subset.
For each category:
- The number of ways to select at least one fruit: \( 6 \) (choose from 1 to 6).
- The number of ways to select at least one vegetable: \( 7 \) (choose from 1 to 7).
- The number of ways to select at least one biscuit: \( 8 \) (choose from 1 to 8).
Step 3: Applying the multiplication principle
Since the selections from each category are independent, the total number of ways is given by:
\[
6 \times 7 \times 8 = 336.
\]
Step 4: Conclusion
Thus, the total number of ways to make a selection while ensuring at least one item from each category is:
\[
\boxed{336}.
\]