You may place a siddur or chumash flat on chair seat or bench on which no one is sitting, but it is an act of piety to stand it up on its edge. 
To sit on a bench or other seat where a holy book rests, raise the book up at least a little; a single piece of paper is sufficient elevation.
NOTE If you are sitting on a bench and someone puts a holy book on the bench, you must stand up or raise the book off the bench. You may not stand a siddur, chumash, or other holy book up on its edge on a bench or pew in order to be allowed to sit on that bench.

You may not acquire items (kinyan) on Shabbat unless they are needed for that Shabbat or for doing a mitzva. The classic example of doing something for Shabbat is bringing food or drink to a house for Shabbat lunch, which the house owner acquires on Shabbat for Shabbat. Other permissible kinyan on Shabbat:

•  Giving a siddur or chumash to use on that Shabbat.
•  Giving permissible medicine for use on that Shabbat.

You may not acquire items (kinyan) on Jewish festivals unless they are needed for that Jewish festival or for a mitzva. The classic example is bringing food or wine to a house for Jewish festival lunch, which the house owner acquires on the Jewish festival for the Jewish festival. Other permissible kinyan on Jewish festivals is giving:

• Siddur, machzor, or chumash to use on that day.
• Permissible medicine for use on that day. 

On bringing mail or a newspaper into your house on Jewish festivals, see Jewish Festivals: Bringing Mail inside House  and Jewish Festivals: Bringing Newspaper inside House.

You may use tzedaka (ma'aser) money to buy seforim. Because the books then become public property, you must write in the books that they are ma'aser and anyone may use them. You may only do this if other people who are not in your family will also use them. 
Note You may only use tzedaka (ma'aser) money to buy seforim that are not commonly found in Jewish homes; you may not use this money to buy a siddur, chumash, or Talmud.