For me, I separate how I feel from the equation. How I feel is merely information about where I have problems or need to work; it's information but not actionable in and of itself.

When I feel I don't matter, I don't find that "helpful" to much. It meerely says to me that I need to go make some connections and get some support from others. One can only "matter" if one is helping and/or interacting with others? I find something concrete to do that someone else appreciates my doing. My husband always thanks me when I make him dinner :-) so often I take the "easy" way out and think of a dinner I know he likes and make it for him. Then I feel good that I've made him a bit happier, made his day a bit more enjoyable. Yesterday his business partner was over and they were sitting on the deck talking after having a little lunch my husband made them because I wasn't feeling very well. I had put some ice cream in the refrigerator so it would get soft so they could have strawberry shortcake :-) I called down to my husband from the balcony to do something with the ice cream in the refrigerator so it wouldn't melt too much. Nothing happened :-) So, I went down and made them each plates of strawberry shortcakes and sat out there with them while they ate it. I actually felt physically better after having done that. I'm sure they're enthusiasm and pleasure in my having made the the shortcake and their expression of it to me, helped me feel better!

Do something, anything. There's a quote I like about not being able to steer a car/vehicle/sailboat that isn't moving. When I feel badly about myself, I "move" and see what happens.

I get angry when I'm anxious. It could be you get angry to keep from being depressed about something specific. When I'm angrier than I like or about something "small" so the anger is out of proportion or angry about something that doesn't "deserve" anger, I stop and use the anger as a "red flag" for myself. I instantly look to see what is making me anxious, where I feel "helpless". Knowing that someone I love is sick or having a hard time or is angry at me, etc. and that I don't feel I can do anything about it sometimes is all I need to get rid of the inappropriate anger. Too, I look at what is actually bothering me and see if there isn't something I can do to make myself feel better. I tell someone else I love about the sick friend/loved one and get comfort from their knowing and caring about me and my friend; I do some little but important thing (call the sick person, send a card, etc.) like call the person I think is mad at me and see if we can't work through the problem or just check out whether they're actually mad at me. I often forget to "reality check" with another person and just go with my own feelings, not asking the person how they're feeling or what they're thinking but just assuming things that may/may not be true.

Pickle, I don't think you have no value, you are not a waste of space and time. Sometimes I just take someone else's word for "it" and accept that I'm seeing things wrong at the moment. It doesn't mean that I "always" see things wrong or that I always will continue to see things wrong in this instance. I put a particular feeling in context, the context of space and time. Feelings change, they're just feelings! Just as we can imagine things, we can "feel" things that aren't based in "fact". It does not mean the feelings are not valid; they're very important because they're information only you can give yourself! But sometimes I just "assume" from what others I trust say that what I feel is not quite right. So, in your case, I would assume that I do have value. Making that assumption, I would then go look for where/how I have value. My focus changes from the negative to the exploratory and that's not quite so bad, it's even kind of "interesting" and hopeful. When I have a really hard time finding anything of value in myself, I ask my husband about me :-) He tells me why he likes/loves me and what good attributes I have and I take his word for it because I trust his judgment. Knowing I have X or Y attribute, I then look for what the other person sees, why they say that. Anything else besides accepting what another says means the other person is a liar? If someone says I'm "kind" (my T told me I was) then my rejection of that for any reason says the other person either doesn't know what they are talking about or they are lying! I would rather just take it that what they say they see in me is "true" (at least for them) and go on from there, patiently looking for indications I can see/understand that I have that attribute.