What homemade items igredients make clothes whiter?

lemon juice works great! Peroxide does as well!

Remove stains from clothing, curtains, and tablecloths. Hydrogen peroxide can be used as a pre-treater for stains — just soak the stain for a little while in 3% hydrogen peroxide before tossing into the laundry. You can also add a cup of peroxide to a regular load of whites to boost brightness. It’s a green alternative to bleach, and works just as well.

Borax or detergent with added whitener. Some countries use lye soap. Hang on clothesline not a dryer.

stop using fabric softener; if you are speaking of 100% cotton, wash with NO detergent for several washes, -- 3-4 cycles; then on the last cycle add appropriate amount of 5% Clorox -- plain -- no scent, etc.

dry on low or hang on the line; Synthetic fabrics may yellow with 'age' or using too high a setting on the dryer.

Landsharkinnc is right about older synthetic white fabrics sometimes aquiring a yellowy look. If this 'staining' has already been set by washing or drying in high temperatures, it can sometime be very difficult to remove entirely.