There are many cases where the article is either optional or forbidden in French, this is usually called article zéro, article nul, or article ∅.
Hospitalité pour deux nuits
is a nominal group where both Hospitalité and deux nuit are lacking an article. The fact this sentence lacks a verb too shows it is something like a book title, chapter name, information panel, advertisement, or point form format where omitting the initial article is often the rule.
Just like with your second sentence which contains a verb, L'essence coûte très cher en France, an article would have been mandatory in:
J'ai demandé l'hospitalité pour deux nuits.
A second article is still optional and would slightly change the meaning of the sentence:
J'ai demandé l'hospitalité pour les deux nuits
Here these are specific nights, not two nights in general.