I'm sorry for your loss. When I first moved out on my own, this book was extremely helpful:
https://www.amazon.com/Going-Solo-Kitchen-Persuasive-Alone/dp/0375703934
Some basic tips, find creative ways to use leftovers. Roast chicken can become soup, potpie, sandwiches, salads, etc. Waste management is the biggest challenge, don't buy more than you can eat. One of the hardest things to keep fresh are vegetables, consider buying frozen and only heating individual servings.
Here's an easy, cheap dish I really like.
Boil water for pasta, cook pasta per directions on box. This can be any small shape pasta, I use farfalle but anything would work. When you add the pasta to the water, start sauteing some garlic in a pan with olive oil. Add your protein, which can be a can of tuna, some sliced deli ham or turkey, some diced bacon, etc. Get it nice and browned and crispy and add a splash of white wine or lemon juice. Add a quick cooking vegetable - spinach, frozen peas, etc, and a spoonful of capers. Drain the pasta, add to the pan and toss, and you have a tasty full meal.
Best of luck to you
I got Going Solo in the Kitchen years ago. It's a great guide to cooking and meal planning for one or two people. It really helped me cut down on costs.
I cook enough for a few meals and then I'll bring it for lunch through the week. This cookbook is helpful for figuring out proportions for meals that will serve one or two people: https://www.amazon.com/Going-Solo-Kitchen-Persuasive-Alone/dp/0375703934 I really appreciate the recipes for baking small servings of cookies and batches of brownies!
And just for fun, I've also enjoyed these two books about eating alone: https://www.amazon.com/Pleasure-All-Mine-Selfish-Modern/dp/006168712X https://www.amazon.com/Alone-Kitchen-Eggplant-Confessions-Cooking/dp/1594483132
I had this book when I was single: http://www.amazon.com/Going-Solo-Kitchen-Jane-Doerfer/dp/0375703934/ref=pd_sim_b_2
Not only is it full of one-friendly recipes, it's also a really, really well-done cookbook. I'd highly recommend it.