Baby steps! You didn't become a smoker and put on 70 pounds overnight. You've developed habits that need to be broken.
Don't focus on weight loss. Focus on your health. Walking will help your cardiovascular health. Rather than looking for what to omit from your diet to help you lose weight, think about what you can substitute for health purposes. Look at that baked potato for lunch and instead of thinking how many calories it will have with butter and sour cream on it, think about substituting salsa for the butter and sour cream. Bam...now you've got fiber from the potato skin (good for GI/colon health) and plenty of lycopene from the salsa (good for eye health).
DH & I have lost over 100 pounds combined. We walked and focused on health and nutrition. We learned about what foods are good for the heart, the skin, the immune system, the GI system, the bones ... all of it. We walked every day -- nothing big. Just walked our dogs A LOT

We looked at nutritional labels and ingredients on food packages. If it contained things like high fructose corn syrup and partially hydrogenated oils, we didn't eat it. We'd either buy something else altogether or learn how to make that particular food ourself without all the chemicals.
And we didn't do all of this overnight. We started with baby steps. First we tackled breakfast and changed out Pop-Tarts or Captain Crunch for fruit, cottage cheese, or oatmeal. Once we felt good and satisfied with our new healthy breakfasts, we moved on to lunch. Then dinner once we felt good about our changes to our lunches.
I realize being at university may have its challenges for finding healthy foods, but you're smart and you have resources available to learn about nutrition.
I know it's hard to look into that crystal ball and see the future, but I really wish I'd taken better care of myself in my 20s.
The smoking I can't help you with. I still smoke. I tackled the weight first, and now I'm tackling the smoking. I never succeeded trying to lose weight and quit smoking at the same time. DH, DM and I all have our Chantix in hand, and we're going to quit together