Like the other answer to this question says, I believe that the gifts the shepherd offers his love are meant to be hyperbolic representations of his love. In other words, one should not view the gifts mentioned in the poem as literal offerings, but as exaggerated examples of the idyllic and idealized nature of the shepherd's love. Take, for instance, the fifth stanza:
A belt of straw and Ivy buds,
With Coral clasps and Amber studs:
And if these pleasures may thee move,
Come live with me, and be my love. (17-20)
Consider the gift mentioned here, the "belt of straw and Ivy buds." Clearly, this belt would be pretty impractical; ivy and straw are not materials destined to last long when worn. Furthermore, clasps made out of coral and amber would not be terribly comfortable. However, the shepherd is not actually imagining that his love will wear this impractical belt. Instead, he's using fanciful and exotic gifts as symbolic images of his idyllic love. As such, the gifts themselves are not terribly important. What's important here is the idealized love symbolized by the gifts. In that case, I definitely think that the gifts are not meant to be taken literally, but instead are meant to be examples of an idealistically romantic love.