First, I think the second sentence is wrong. It should be, "What we can do is offer you meal vouchers." Whether to use "to + verb" or not depends on whether a verb or noun needs to come after "is." If a verb [i.e. action] needs to come after "is," don't use "to." EXAMPLE: What they should do is _________ [they need to do an action/verb] What they should do is impose restrictions. [impose = verb] If a noun [i.e. thing] needs to come after "is," use "to + verb." EXAMPLE: What I'd really like is _________ [noun] What I'd really like is a book. [book = noun] What I'd really like is a nap. [nap = noun] What I'd really like is to lie by the pool. [to lie = noun] REASON: "to + verb" is called an "infinitive." Infinitives are verbs that act like nouns.