If you are not attending a shower, you don't have to send a gift. Whether or not you attend the wedding, a gift is optional. That's the stance of all etiquette mavens of any repute.

On the other hand, it is certainly in no way improper to send a gift to either or both of these functions should you wish to do so.

As for what to give, if you know where the happy couple is registered (if they are), you can easily check their registry list for ideas. If there's nothing on the list that you can afford/would like to give, at least you'll have an idea of what they don't have for their household or what colors they plan to decorate with.

If these people are truly your friends, they won't be offended by the gift(s) you choose. They know your circumstances and know your friendship.

One of our wedding guests had very little money to spend, so she got us some inexpensive measuring cups and spoons at an import store. She probably spent a grand total of five dollars on her gift, if that. But fourteen years later, I'm still using those measuring cups and spoons and thinking of her when I do because I know how much those couple dollars cost her at a time when money was very tight.

Good friends know it's the thought rather than the pricetag that counts.