For example,I want to tell a memory of past tense and explain how i used to take shower in wild camping.Is "used to" the only option? Is it Ok to use simple past tense? I've learnt English through reading books and don't know much about grammar.
You are looking for a tense to describe repeated actions/states in the past. This is called the past with habitual aspect or habitual past, which can be expressed in several ways:
Simple Past [with Adverb]
Whenever I visited my grandmother, I [always] brought her a box of chocolates.
Whenever I‘d visit my grandmother, I’d bring her a box of chocolates.
I used to bring my grandmother a box of chocolates whenever I visited her.
As Jesse Williams pointed out, you can be quite literal about it and remember performing some action at least twice in the past:
I remember bringing my grandmother a box of chocolates every time I visited her.
Simple past tense is by far the most common, but I suppose it depends on your usage. If you're writing creatively or in a way which lends itself to building a scene, you could go with a descriptive route. Something like:
I recall many times showering in the wild or bathing in the lake, the sun low on the horizon.
Making the primary verb past tense works just as well, and often better, than going with used to.