Accusative preposition = in/ins

I understand that “ins” is a contraction for “in das” which means you can write a sentence like “He goes into the car” like “Er geht ins Auto”, as an alternative to “Er geht in das Auto”, which is easy way to apply the preposition “in” in the accusative case form.

1. Can you do something similar with “der / masculine form”? e.g.
English: He goes into in the bus
German: Er geht in den Bus -> Is there any contraction possibility here?
 
2. Can you do something similar with “die / feminine form”? e.g.
English: She puts it into the box
German: Sie liegt es in die Kiste - > Is there any contraction possibility here?
 
3. Any contraction for “plural form”?

Hallo RexV!

Regarding your example, note that the separable verb einsteigen is usually used for getting into a vehicle, so it would be Er steigt ins Auto ein "He gets into the car."

There aren't any contractions between in and den or die, however, so none for the masculine, feminine or plural forms.

Be sure to keep in mind that the contraction ins for in + das is standard, so Er steigt ins Auto ein shouldn't really be thought of as an alternative to "Er steigt in das Auto ein"; rather, it is the preferred form (unless, as we've said before, das is being emphasized for some reason). 

Tschüss!

Liss