What do you tell yourself everyday to keep you going?

Hello and thank you for asking a question here on BetterHelp. I'm sorry to hear you have been struggling with anxiety and depression, and having those days where you just don't feel like you can keep going. First of all, I would like to commend you for reaching out and asking for help, and second I would also like to commend you for having good insight. You are aware that these hard days suck and you want to do some thing to make them easier. It's good that you recognize and believe you could make changes to make those hard days more tolerable. I have a few suggestions I think could really help but I also think it's important that we talk a little bit about therapy first.

Going through ups and downs like this is really difficult, and having a professional come alongside to support you can make a massive difference. Because of this I would strongly recommend meeting with a therapist. It's very easy to get linked with a therapist here on BetterHelp, all you have to do is click on the get started button on the homepage and follow the prompts from there. After this you'll be automatically linked to a therapist, if you don't like the therapist you are automatically linked with you are more than welcome to choose one on your own or ask to be automatically linked to somebody else. Meeting with a therapist can help you recognize barriers in your life you didn't know existed but stopping you from being the person that you want to be, a therapist can help you recognize toxic behavior in your own life that you made if that was completely normal. A therapist can also help you recognize what relationships in your life are holding you back and what relationships are helping make you a better person. I know therapy can seem expensive at first but I can also make a massive difference in improving your life and becoming the person you want to be, I hope you'll consider getting linked with a therapist soon. 
When it comes to handling hard days there are two things that you can do. They are both of equal importance, the first thing you need to do is to fill up a very healthy support system. This means having a therapist that you can turn to, this also means having good and trustworthy friends you can turn to and say, "hey I'm having a really difficult day today, can we spend some time together?" But I would also argue that the support goes well beyond people, there are many ways you can support yourself as you go through this. When you're feeling down like this it can be an amazing time to do some journaling, doing so will help you better understand your difficult times so you can help prevent them in the future. Another good technique while you are journaling is to write down a gratitude list, it's something that is very difficult to do when you are feeling down but can also help lift you out of feeling down. I have personally seen gratitude lists change peoples lives multiple times. When you were feeling down those reminders of why you should be grateful and reminders of things to be grateful for can lift your spirits. But let's say you're not into journaling, it will be an excellent time to try and practice some artwork or some other hobby that can help lift your spirits. All of those are different forms of support that you can rely on from others and rely on yourself for. We want you to have a plan for those days where you are really struggling, if you are able to execute that plan then you take control over your bad days instead of your bad days having control over you. 
The second thing you can do is make sure that your life is firing on all cylinders on your good days. This means practicing good self-care, I always explain to people that self-care is hard and takes practice. People often confuse treating yourself and self-care, but they're not even remotely the same. Good self-care means making smart financial decisions and preparing for the future, it means taking good care of your body and watching what you put into it, good self-care means recognizing toxic behavior in your own life and making an active effort to change it, it also means recognizing toxic relationships and making an active effort to stay away from those relationships. Doing this will help you make sure your life is headed in the right direction at all times.

The last thing I want to leave you with is something I tell everybody that I work with and I think goes along well with the second thing. There are three things that everyone needs in their life for some satisfaction. The first thing we need is a caring community, I talked a little bit about this earlier; it means having good and trustworthy friends in your life and also means being a good and trustworthy friend. The second thing is productivity, we are not meant to sit on the couch all day and flip through our phones on social media or watch Netflix. Being productive releases endorphins in your brain which makes you feel better and motivates you to be more productive. You can be productive through employment you find purpose in, education, volunteering, exercise, tidying up your living space, or even cooking a good meal for your self or meal prepping. We thrive off being productive. The third and final thing that we all need is high-quality rest, this means having something in your life that you do just for you simply because you want to. We all need some sort of hobby or activity that we do and are looking forward to that recharges our batteries. Life can't be all productivity. For me it's being in the outdoors and traveling, it motivates me on difficult days and gives me something to look forward to. Do you see any area out of these three that need improvement? I hope you were able to find something in here that helps and I wish you the best of luck!